(C) P. Meakin 1998-2004

This product is licenced to St. Mary Redcliffe and Temple CE School .

Use and reproduction of this booklet is permitted within the institution named above, subject to the restrictions set out in the online licence agreement. All other rights are reserved by the author.

1.1. Information And Data : Introduction

Computers do not work with information. Information is something which has a meaning. As computers are machines they can not understand the meaning of sentences like "Jane was born on the 14/06/75". Instead computers just store sequences of letters and numbers. They do not know what these sequences mean. The sequences which the computer stores are called data.

• Information : Something which has a meaning to a human being.
• Data : Numbers, words etc. which have no meaning by themselves.

Here are some examples of data and information :

Data can become information when it is given a context. For example :

• The word "Sausage" is data because it has no meaning by itself. It does not tell us anything. But when it is placed in the context of the sentence "The sausage is hot" it does tell us something (that the sausage is hot), so it becomes information.
• The number 190387 is data, but when it is placed in the context of being John's date of birth (the 19th of March 1987) it becomes information.

The link between information and data is often described like this :

Information = Data + Context

1.2. Information And Data : Types and Knowledge

Information can be quantitative or qualitative :

Knowledge is the information, skills and experiences that have been learned by a human. New knowledge can be created from existing information by applying logical rules to the information. For example if we have the information :

John is Michael's brother.            Michael is Mary's brother.

and know the logical rule that :

If person A is B's brother and B is C's brother then A is also C's brother.

Then we can reason that John is also Mary's brother. We have created new knowledge from information by applying rules. Reasoning with information to produce knowledge is one way of processing information, so knowledge is sometimes described as :

Knowledge = Information + Processing

1.3. Information And Data : Storing and Coding

Converting information into data that a computer can process and store is known as coding information. Here are some examples of how information can be encoded as data :

Coding reduces the amount of data storage space required, can speed up the process of typing the information in and makes it easier to validate (check) data. For coding to work properly everyone who uses an information system needs to know what the correct codes are.

In fact most computers are digital devices and can only store the numbers 0 and 1 in their memories. Letters and other numbers must be encoded as sequences of 0s and 1s (called binary) before they can be stored. This encoding is done automatically by the computer.

Decimal numbers are represented in binary by sequences of 0s and 1s :

Letters and symbols are stored in binary using a standard coding system such as ASCII. Each letter is represented by a unique pattern of 0s and 1s :

1.4. Information And Data : Presenting Information

You may need to pass information that you have onto another person. When this happens you must choose how to present the information to make sure that the other person understands and remembers it. The same information can be presented in many different ways. For example :

The best way to present information will depend upon :

• The purpose that the information is being used for.
• Who the information is being presented to.
• What facilities you have to help you present the information.

This table shows how the same information can be presented in different ways when used for different purposes :

Some audiences may have special needs, so the method used to present information may need to be tailored to these. For example :

Computer software such as a word processor, desktop publisher, spreadsheet or graphics package can be used to help present information. Information can be presented on paper as a hard copy or on screen in the form of a multimedia presentation.

Information systems present the results of processing using an output device.

1.5. Information : Summary

2.1. Information Systems : Introduction

Information is stored and used by organisations such as the government, companies and clubs for a variety of purposes. Some examples of people who store and use information are :

When a system has been set up to store and carry out tasks using information we call this an information system. Today most information systems use computers, but this has not always been the case and some information systems are still operated manually.

• Manual Information Systems : Diary, Address Book, Filing Cabinet.
• Computerised Information Systems : Stock Control System, Flight Booking System.

When we talk about computerised information systems we can use a better definition of the term information system :

An information system consists of everything needed to perform a particular task using information. This will include hardware, software and the people who use the system.

2.2. Information Systems : Model

This model can be used to describe the operation of any information system.

The model has three essential components :

• Input : Information going into an information system.

• Processing : Organisation and manipulation of data by an information system.

• Output : Information produced by an information system.

Most information systems also have a fourth component :

• Store : The ability to remember information temporarily or permanently.

Information systems usually include many inputs and outputs. The next pages contain two more detailed examples of information systems.

2.3. Information Systems : Exam Grades Example

Description of System

A teacher uses a spreadsheet package to help her analyse the results that her students have obtained in their GCSE Information and Communication Technology mock examination. The teacher enters the names of each student into her spreadsheet. She also enters each student's percentage scores in two different exam papers.

The teacher must decide what average mark a student will need to obtain to get a particular grade on his or her end of year report. For example she may decide that anyone who scores above 80% will get an A, anyone with a score between 70% and 80% will get a B and so on. The dividing point between two grades is known as a grade boundary. The grade boundaries must also be typed into the spreadsheet.

The spreadsheet then calculates the students' average scores and gives each student a grade based on their average. At this point a report is printed for each student to inform them of their marks and grade.

The spreadsheet now performs some further processing. It sorts the students into order so that the student with the highest mark is at the top and the student with the lowest mark is at the bottom. The teacher then prints this list for her own records.

Here is the spreadsheet that the teacher uses :

Identification of Outputs, Inputs, Processing and Storage Requirements

From this description of the system, it is possible to identify what the outputs, inputs, processing and storage requirements of this system are. They are summarised in this table :

Outputs	A report for each student showing scores in each paper, average score and grade.
	A list showing the marks and grade of each student in ascending order of mark.
Inputs	The names of the students.
	The scores of each student in the two examination papers.
	The grade boundaries for each grade.
Processing	Average the marks of each student in the two papers.
	Award grades based on the students' average marks.
	Sort the list of students into ascending order by mark.
Storage	This system does not need to store any data permanently, but the teacher will probably find it useful to save the spreadsheet so she can reuse it later.

Diagramatic Model of System

This system flowchart shows the structure of this information system in diagram form :

2.4. Information Systems : Stock Control

Description of System

A small store uses a very simple stock control system. The system stores the details of all of the products that the store sells. These details are kept in a stock file on a magnetic disk. Each product that the store sells can be identified by a unique product code.

When a customer takes her shopping to the checkout the checkout operator inputs the product code numbers from the items that are being purchased using a bar code reader. If a product code is scanned correctly then the till beeps. If the code is not scanned correctly then there is no beep so the operator knows that the bar code must be rescanned. If the code will not scan a second time then the operator must manually type the product code into the till using a keyboard.

When a code is successfully entered, the checkout looks up the product code in the stock file. From the stock file the name of the product and its price is obtained. This information is printed on the customer's receipt and the total cost of the purchases is calculated.

At the same time the record that the computer keeps of how many units of each product are in stock is amended to show which items have been sold. At the end of the day the checkout will print a list of the items that are running low on stock so that they can be reordered.

Identification of Outputs, Inputs, Processing and Storage Requirements

From this description of the system, it is possible to identify what the outputs, inputs, processing and storage requirements of this system are. They are summarised in this table :

Outputs	Itemised till receipt for each customer.
	Buzzer noise when a product code is scanned correctly.
	List of products which need reordering to be printed at the end of each day.
Inputs	Product code of each product that is sold to be entered using a bar code reader or keyboard.
	List of all of the products that the shop sells to be entered when the system is first set up and amended later as necessary.
Processing	As products are sold look up product codes in stock file. Print item names and prices on receipt and add up totals.
	Monitor how many units of each product are in stock by reducing the stock level of an item when it is sold.
Storage	A stock file will be held on magnetic disk. For each product the shop stocks this file must contain : The product's code. The product's name. The product's price. How many units of the product the shop has in stock.

Diagramatic Model of System

This system flowchart shows the structure of this information system in diagram form :

2.5. Information Systems : Feedback

In some information systems, the outputs that the system produces can generate further inputs. When the outputs of a system affect its inputs we say that feedback is occuring. Our model can be extended to incorporate feedback like this :

Feedback occurs in two different types of information systems :

System Type	Explanation
Control Systems	Computerised control systems use sensors to gather data. They switch devices on and off based on the data gathered. A control system for a greenhouse could incorporate a temperature sensor which measures the temperature in the greenhouse and a heater to warm it when it is cold. When the system detects it is cold the heater is turned on. This changes the temperature. The output (heat) affects the input (temperature) so feedback occurs.
Turnaround Documents	Some information systems produce as output forms which the user must fill in. When the user has completed a form the extra information added onto it is entered into the computer. These documents are known as turnaround documents. Because the completed output forms are used to produce new inputs feedback occurs.

2.6. Information Systems : Why Computerise?

Why Computerise An Information System ?

Most organisations use computerised information systems instead of manual systems. Computerised systems have many advantages. Three of the most important reasons for choosing to use a computerised system are :

• Storage : Computerised systems can store vast amounts of data in small spaces and retrieve this data very quickly.
• Processing : Computerised systems can manipulate and analyse data very quickly and accurately.
• Networking : Data can be quickly and easily passed around the world electronically and shared between different companies.

This table lists some examples of how these advantages are useful to organisations.

Why Not Computerise An Information System ?

Despite all of these advantages some manual information systems are still used. These systems are often kept because :

• For small information systems (e.g. an address book) data can be retrieved from a manual system quickly enough and no sophisticated processing is needed.
• The cost of purchasing the hardware and software required to create a computerised system together with retraining users can outweigh the advantages of a new system.
• If a current manual system is working well and users are happy with it then it may be difficult to persuade users to change to a new computerised system.

2.7. Information Systems : Summary

3.1. Hardware : Introduction

A computer system will input, process and then output data. A computer system consists of the computer and other hardware devices that are used with the computer. A hardware device is an electronic or electro-mechanical device such as a keyboard or monitor which forms part of a computer system.

The diagrams below show one simple and one more complicated computer system.

The devices connected to the computer can be divided up into three different classes :

Some devices such as disk drives, modems and CD-ROM drives are now built into the same box as the computer. This helps to keep computers tidy. Devices connected to a computer are often known as peripherals.

Computer hardware is not very useful by itself. The hardware needs to be told what to do. A computer program contains instructions to tell the computer hardware what to do to carry out a particular task. Computer programs are produced using a programming language. Computer programs are also known as software. The most important piece of computer software that a computer system must have to function is an operating system. Other useful pieces of computer software include word processors, spreadsheets and databases.

3.2. Hardware : Inside a Computer

There are separate articles on the many different items that could be included in a computer system. As a starting point, here is a brief list of the components that you would expect to find inside a typical computer :

• A microprocessor that can carry out arithmetic and logical operations on data.
• Some RAM that will store temporarily the programs and data that the user is currently working with.
• Some ROM to store the BIOS program that is run when the computer is first turned on.
• A hard disk drive that will store the programs that the user has installed and any files that he has created.
• A floppy disk drive and CD-RW or DVD drive that can be used to install software and to transfer files from one computer to another.
• A modem that can be used to send data over a telephone line to access the Internet.

Computer systems are designed to be flexible. It is usually possible to expand the capabilites of a computer by replacing or upgrading internal components or connecting extra devices externally. External devices are connected to a computer using sockets known as ports.

3.3. Hardware : Types of Computer

There are three main types of computer. They are :

• Microcomputers
• Minicomputers
• Mainframe Computers

Microcomputers (also known as PCs) are the smallest and cheapest of these and are used at home, in schools and in some businesses. Most PCs contain just one microprocessor.

Mainframe computers are the most powerful computers. A mainframe computer may contain several microprocessors. Computers which contain more than one processor are capable of doing more than one thing at a time and are described as being capable of parallel processing. A single mainframe computer can be used by hundreds of people at once. Each user has his own terminal that is connected to the mainframe. Mainframe computers are usually kept in a special cooled, clean computer room. Today many businesses are getting rid of their mainframe computers and replacing them with networks of smaller microcomputers.

Minicomputers were medium-sized computers that were more powerful than microcomputers but not as powerful as mainframes. Minicomputers where phased out in the 1990s as microcomputers became more powerful.

This table makes some comparisons between the different types of computer :

Comparisons of Computer Types
Comparison	Microcomputer	Minicomputer	Mainframe
Where Used	Home, small business, on a network in a larger business.	Medium sized business. e.g. supermarket, traffic control system.	Large businesses, universities.
Number of Users	1	1-20	Hundreds
Cost	£200 - £10,000	Not Available	£150,000+

A Supercomputer is a very fast mainframe which may contain many hundreds of microprocessors.

3.4. Hardware : Microcomputers

A microcomputer is a computer that is based around a microprocessor. The most common type of microcomputer is the Desktop but there are a number of other types as well :

3.5. Hardware : Summary

1.	A computer system will input, process and then output data.
2.	A computer system consists of the computer and other hardware devices that are used with the computer.
3.	A hardware device is an electronic or electro-mechanical device such as a keyboard or monitor which forms part of a computer system.
4.	The devices connected to the computer can be divided up into three different classes : Input Devices, Output Devices and Input/Output Devices.
5.	Devices connected to a computer are often known as peripherals.
6.	Computer hardware is not very useful by itself. Software is required to tell the hardware what to do.
7.	Computer systems are designed to be expanded, but a typical computer will have these items inside it when it is purchased : A microprocessor that can carry out arithmetic and logical operations on data. Some RAM that will store temporarily the programs and data that the user is currently working with. Some ROM to store the BIOS program that is run when the computer is first turned on. A hard disk drive that will store the programs that the user has installed and any files that he has created. A floppy disk drive and CD-RW or DVD drive that can be used to install software and to transfer files from one computer to another. A modem that can be used to send data over a telephone line to access the Internet.
8.	There are three different types of computer. They are : Type Description Microcomputer/PC A single user computer which contains a microprocessor. Minicomputer A medium sized computer system used by 1 to 20 users. Mainframe A very powerful computer which may be used by hundreds of users.
9.	A supercomputer is a very powerful, very expensive mainframe containing hundreds of microprocessors.
10.	There are four different types of microcomputer. They are : Type Description Desktop A general purpose computer which can be connected to many peripherals. Laptop A small computer which is portable, battery powered and incorporates a computer and common peripherals in one device. Palmtop or PDA A very small computer which is handheld and can fit in a pocket. Often supplied with organiser software such as a diary and address book. Games Console A microcomputer designed specifically to play computer games. Embedded System A computer system that forms part of a larger device such as a car and can only be used for one specific purpose.

4.1. Input Devices : Introduction

An information system can not do anything until you give it some information to process. Input devices transfer data into a computerised information system so that it can be processed.

An input device transfers data from the outside world into a computer.

There are two different categories of input device. They are :

• Manual Input Devices : With a manual input device the user must enter data into the computer by hand.
• Direct Data Entry (DDE) Devices : A direct data entry device can transfer information automatically from a source document such as a form or barcode into the computer. The user does not need to manually enter the information. Direct data entry devices are used when large volumes of data must be entered into the computer quickly.

There are many different input devices available. Each input device is suitable for a different purpose. Select an input device from the table below to find out about it or read through the rest of this topic to learn more about all of the different input devices.

Manual Input Devices
Keyboards	QWERTY Keyboard
	Concept Keyboard
Pointing Devices	Touch Screen
	Light Pen
	Mouse
	Tracker Ball
	Touch Pad
	Joystick
Graphics Capture	Graphics Tablet
	Scanner
	Digital Camera
	Video Capture
Sound Capture	Voice Recognition
	MIDI
Others	Remote Control
	Biometric Devices
	Sensors
Direct Data Entry (DDE) Devices
Code Numbers	Bar Codes
	Magentic Ink Character Recognition
	Magnetic Stripe Codes
	Smart Cards
Optical Input Methods	Optical Mark Recognition
	Optical Character Recognition
	Turnaround Documents / PDET

4.2. Input Devices : QWERTY Keyboard

Almost all general purpose computers are supplied with a keyboard. A keyboard has over 100 keys on it. When you press a key a number (code) is sent to the computer to tell it which key you have pressed. The keys are arranged in four groups :

The keys on a keyboard are usually arranged in the same order as those on a typewriter. This layout of keys is called QWERTY because Q-W-E-R-T-Y is the order in which the letters occur on the top row of the keyboard. Some newer designs have the letters arranged in a different order. Most people find the QWERTY arrangement best as they have had some practise using it, but some users trained on the new keyboards claim that they can type faster than the fastest typists can on QWERTY keyboards.

4.3. Input Devices : Concept Keyboard

A concept keyboard is a flat board which contains a grid of switches. Each switch can be programmed to do whatever you want. An overlay image is placed on top of the grid so that the user can tell what pressing on different areas of the keyboard (switches) will do.

Example uses of concept keyboards include :

• Piano : The overlay image could be of a piano keyboard. Pressing on the piano keys will cause the computer to play the note that is pressed.
• Country Information : The overlay image could be a map of an area of the world. Pressing on a country would cause the computer to display information about that country on a monitor.
• Tills in restaurants/pubs : The overlay contains a list of all of the meals that can be purchased. Instead of typing in prices the waiter simply presses on the appropriate meal name on the keyboard when a meal is purchased.

Concept keyboards are particularly useful for users such as children who would find using a QWERTY keyboard difficult and in locations where an ordinary keyboard might be damaged, e.g. by spillage or dust.

4.4. Input Devices : Touch Sensitive Screens

A touch sensitive screen is a special type of visual display unit. In front of the display a grid of light beams or fine wires criss-cross the screen. When you touch the screen the computer senses where you have pressed. Touch screens can be used to choose options which are displayed on the screen.

The main application for which touch screens are used is the provision of public information systems. Touch screen operated computers can be found in places such as travel agents and airports. Here a touch screen is being used to provide information to tourists :

The grid in front of the screen can not be seen by the user. The screen is located behind the glass in the tourist office's window so that visitors can obtain information even if the office is closed.

Touch screens are not used very often as they are not very accurate, tiring to use for a long period and are more expensive than alternatives like a mouse. The main advantage of the touch screen is that anyone can use it without having to be trained.

4.5. Input Devices : Light Pen

A light pen is a special pen which you can point at any computer monitor. When the pen is pointed at the screen the computer can work out where the pen is pointing.

Light pens can be used to "draw" on the screen or to select options from menus presented on the screen.

Light pens are extremely poor input devices. They are very inaccurate and tiring to use. Light pens were popular in the 1980s and early 1990s but most have now been replaced with other input devices.

4.6. Input Devices : Mouse

A mouse is the most common pointing device. You move the mouse around on a mat and a small cursor called a pointer follows your movements on the computer screen. By pressing a button on the mouse (most mice have 1,2 or 3 buttons) you can select options using icons or menus on the screen. Mice can also be used to "draw" onto the screen. They are particularly useful if your computer has a graphical user interface.

Most mice use a small ball located underneath them to calculate the direction that you are moving the mouse in. As you move the mouse this ball rotates. The mouse monitors how far the ball turns and in what direction and sends this information to the computer to move the pointer.

4.7. Input Devices : Tracker Ball

A tracker ball (or trackball) is an alternative to a mouse. It operates in the same way as a mouse except that the ball is on top. Turning the ball with your hand moves the pointer on the screen.

Tracker balls are popular when there is not enough space for a mouse, e.g. in portable computers. Most tracker balls have buttons next to them which can be used to select options from the screen.

4.8. Input Devices : Touch Pad

A touch pad is another alternative to a mouse. It is a pointing device which is used in laptop computers. A touch pad is a rectangular pad about 4cm x 4cm in size. You can move your finger around on top of the touch pad. As your finger moves, the pointer follows its movement on the screen.

Buttons are usually placed next to the touch pad. Pressing a button will select an option on the screen just like a mouse button. With some touch pads, if you tap the pad sharply with a finger this will have the same effect as pressing one of the buttons.

4.9. Input Devices : Joystick

Joysticks are popular for playing computer games and controlling computer simulations. You can move a standard joystick in any one of eight directions. The joystick tells the computer in which direction it is being pulled and the computer uses this information to e.g. move a spaceship on screen. A joystick may also have several buttons which can be pressed to trigger actions such as firing a missile.

The best joysticks, called analogue joysticks measure how far the joystick is being moved in the direction it is being pulled. This information is used to set how quickly the object on the screen moves. The further you push the joystick the faster the object moves.

Small joysticks called trackpoint devices are sometimes built into the keyboards of portable computers and used instead of a mouse.

4.10. Input Devices : Graphics Tablet

Graphics tablets are mainly used by professional graphics designers. Using a graphics tablet a designer can produce much more accurate drawings on the screen than he could with a mouse or other pointing device. A graphics tablet consists of a flat pad (the tablet) on which the user "draws" with a special pen called a stylus. As the user "draws" on the pad the image is created on the screen. The pad on which the user draws can be any size from A5 to A1 (eight times as large as an A4 page). Drawings created using a graphics tablet can be accurate to within hundredths of an inch. Graphics tablets are also known as graphics digitisers.

The stylus that the user draws with may have a button on it which will act like a mouse button. Sometimes instead of a stylus a highly accurate mouse-like device called a puck is used to draw on the tablet.

Graphics tablets are often used to provide input to Computer Aided Design packages.

4.11. Input Devices : Scanner

A scanner can be used to input printed images such as photographs or pages of text directly into the computer. A scanner works by shining a light at the image being scanned and measuring how much light is reflected back using an optical sensor. The amount of light that is reflected back tells the computer how light or dark the image is at each point.

Optical Character Recognition (OCR) software can be used to read printed text from an image that has been scanned and store it as text rather than an image. You can then edit the text using a word processor or desktop publisher. OCR software is not yet sophisticated enough to read hand-written text accurately.

4.12. Input Devices : Digital Camera

Digital cameras are used in the same way as standard photographic cameras. Most digital cameras look just like ordinary cameras. Unlike photographic cameras digital cameras do not use film. Inside a digital camera is an array of light sensors. When a picture is taken the array of sensors is used to input the image. The image can then be stored either in the camera's RAM or on a floppy disk. Later the pictures can be transferred onto a computer for editing using a painting package.

Digital cameras are available from about £30 upwards. The quality of the pictures that a camera can take depends upon the resolution of the camera. This is measured in millions of pixels (megapixels). Modern cameras have resolutions from about 1 to 5 megapixels. Digital cameras are extremely useful for tasks such as producing newsletters. The images can be transferred directly into a desktop publisher without having to be developed, printed and then scanned.

4.13. Input Devices : Video Capture

Computers store videos as a sequence of still images called frames. These images are displayed quickly one after the other (rather like a flick-book) to create the illusion of a moving picture. Inputting a video into a computer is known as capturing the video. When you want to capture a video sequence you must tell the computer :

• Size : How big you want the image you capture to be. e.g. should it take up the whole screen, 1/2 the screen, 1/8th of the screen ... ?
• Frame Rate : How frequently the frames should be captured from the video.

If you want to capture large images you may have to settle for a slow frame rate which will make the captured video film look jittery. If you want a fast frame rate you may only be able to capture a small image size.

The three most common devices that can be used to capture videos are :

Video Digitiser	A video digitiser takes an image from a video camera or television and converts it so that it can be stored on a computer. Video digitisers can capture large images at fast frame rates. Many video digitisers now incorporate a television tuner so that television pictures can be captured directly.
Web Camera	A web camera captures video images for transmission over the Internet. Web cameras capture small images at a slow frame rate. They are cheap to buy.
Digital Camera	Most digital cameras that take photographs can also capture short video sequences.

4.14. Input Devices : Voice Recognition

Voice recognition systems listen to what people are saying and carry out the instructions given to them when people speak. A microphone is used to provide input for a voice recognition system. Currently these systems are not very sophisticated and are used only for certain applications. Existing voice recognition systems come in two different types :

• Systems which recognise only a few words but can understand most peoples voices. e.g. telephone banking computers.
• Systems which recognise a wide vocabulary but need to be trained to understand each different voice. e.g. automatic dictation systems.

In the last few years a number of voice dictation packages have been developed. These packages let the user dictate text into a computer to appear in a word processed document. Dictating like this can be much quicker than typing but the computer still makes some mistakes especially with short words and with words that sound the same but are spelt differently. e.g. there and their.

4.15. Input Devices : MIDI

The Musical Instrument Digital Interface (MIDI) system allows a musical instrument to communicate with a computer system. The musical instrument acts as an input device to the system. As it is played computer software records information about the duration, pitch and volume of each note.

Music input into a computer by a MIDI instrument can be saved or edited by the user. It can also be printed out as a musical score. The computer can play the recorded piece of music either through its own speakers or through a MIDI instrument that is being used as an output device.

Sophisticated MIDI software can receive inputs from up to sixteen musical instruments at once and can play music back on many instruments simultaneously. The various instruments can all be sequenced together so that they play back in time with each other.

4.16. Input Devices : Remote Controls

A remote control is used to operate a machine from a distance. Remote controls are used with consumer devices such as televisions and hi-fi music systems and vehicle locking systems.

Remote controls have a small keyboard on them with buttons that relate to the particular functions of the machine that is being controlled. When the buttons are pressed a signal is sent from the remote control to the machine, usually by infra-red light or radio signal.

It is more convenient to be able to operate a machine remotely than to have to move to the machine to use it.

4.17. Input Devices : Biometric Devices

A biometric input device measures a unique physical chracteristic of a person. The most common biometric devices are used to input a person's fingerprint into a computer. More sophisticated devices use a camera to input a description of a person's iris (the coloured part of the eye).

Biometric devices are usually used for security purposes. A record of a person's fingerprint or iris pattern is stored in a database. Later on the identity of a person can be determined by re-scanning the finger or eye and looking up the results of the scan in the database. Biometric devices provide a very reliable way of identifying people. Real world applications of this include :

Access Control	A biometric security system can control access to computer files or buildings instead of passwords or keys.
Passports	Biometric information can be included in electronic passports, making it much harder for a passport to be fraudulently used.

4.18. Input Devices : Sensors

A sensor is a device which measures a physical quantity such as the temperature and then sends a voltage to the computer representing the quantity. Sensors can be either analogue or digital :

• Digital : Sensors are either on or off. For example a switch of pressure pad.

• Analogue : Sensors can measure a range of values. The size of the voltage the sensor produces is determined by the size of the quantity that the sensor has measured. For example if a cold temperature is measured a small voltage will be sent, whilst if a hot temperature is measured a larger voltage will be sent.

There are lots of different sensors available, each of which is designed to measure a specific quantity. Examples of sensors include :

Sensors are usually used in data logging and control systems.

4.19. Input Devices : Barcodes

Barcodes are often printed on products that you can buy and are used by shops and supermarkets to produce bills for customers. A barcode is made up of a sequence of bars of different widths. Different groups of bars are used to represent different numbers. A printed barcode is therefore simply a way of representing a number. The number is often printed above or below the barcode so that humans can read it.

Barcodes are read into the computer using a wand or a fixed scanner. Barcodes are not easily damaged and can normally still be read if they are creased or not stuck onto a flat surface. They can be printed using a normal printer and ink and so are cheap to produce. The information normally included on a barcode for a product is country of origin, manufacturer and item code. The price is not included in the barcode.

A scanner can read a barcode number incorrectly. A check digit is included in the barcode number to reduce the likelihood of this happening.

4.20. Input Devices : MICR

The Magnetic Ink Character Recognition (MICR) system reads characters printed in a special magnetic ink into the computer. The main users of MICR are banks. They use it to read information from cheques into their computers so that the cheques can be cashed. Here is some information stored on a cheque using MICR :

The information printed on the cheque using MICR is :

• A unique number for the cheque.
• A code that identifies the bank and branch that issued the cheque (the sort code).
• The number of the account that the cheque relates to.

MICR readers can only read one special font which can represent only numbers and a few punctuation marks. They can read characters very quickly and with 100% accuracy. Information printed in magnetic ink is also very secure. It is not possible to change the information by writing over it with a pen and the printed numbers are not damaged by folding (as often happens with cheques). Both the reader used by MICR and the special ink are expensive.

4.21. Input Devices : Magnetic Stripe

Magnetic stripes (or strips) are built into many plastic cards such as cheque guarantee or credit cards. Magnetic stripes look like this :

The strip can contain up to 60 characters (numbers or digits) of information which is stored magnetically. Usually the information is put onto the stripe when the card is made and is never changed. Magnetic stripe codes can also sometimes be found on the back of railway tickets.

To be read the card is swiped through a machine which quickly and accurately reads the pattern of magnetism. The information stored on the card can be destroyed by exposure to magnetic fields, by scratching or by coming into contact with some liquids.

For many purposes cards that incorporate magnetic stripes are now being replaced with smart cards.

4.22. Input Devices : Smart Cards

Smart cards are often called input devices. In fact they are actually simple storage devices. A smart card looks like a magnetic stripe card but it contains a small RAM chip. When the card is put into a machine data can be read from the card or written onto it. A smart card can store much more data than a magentic stripe card can. The most popular card in use at the moment can store up to 4Kb (about 4000 characters) of information but cards with capacities up to 1Mb (1,000,000 characters) are available.

Petrol companies and supermarkets use smart cards to store information about points that customers earn when they buy goods. Every time the customer buys something the number of points stored on the card is increased. The customer can then spend these points to buy goods. Many banks now issue debit cards that are smart cards as these are more secure than traditional magnetic stripe cards.

Some smart cards contain a small microprocessor as well as memory. These cards are practically a complete computer system on a card. They are used for applications such as decoding pictures from satellite television stations.

4.23. Input Devices : OMR

An optical mark recognition (also known as OMR or mark sense) system reads marks made by pencil on a printed form into the computer. OMR systems are used by examination boards to collect the answers to multiple choice examinations and to purchase lottery tickets. Here is an example answer grid for an examination :

The student answers each question by drawing a line in pencil in the box that he/she thinks is the correct one. The answer grid is printed in a special coloured ink called that the OMR system will ignore. Marks down the side of the form are used to automatically line the form up in the reader so that it can be read. The reader detects where the marks are placed by shining a light at the page and measuring the amount of light reflected. Less light is reflected where the marks have been made. A pile of forms collected at the end of an examination can be put into a tray (called a bin). The reader will go through each form in turn and record the candidates marks.

Input using OMR is accurate and very fast. Problems can occur if the OMR forms get creased as the reader may jam.

4.24. Input Devices : OCR

An optical character recognition system consists of a scanner and some software. The scanner is used to scan an image of a page of text to be read into the computer. The software then examines the page and extracts the text from it, storing it in a form that can be processed.

OCR systems can now recognise a wide variety of computer fonts and read letters with over 99% accuracy. Some systems will recognise hand-written text reasonably well as long as it is written very neatly and usually put into boxes on a pre-printed form.

4.25. Input Devices : Turnaround Documents

Optical mark recognition and optical character recognition are often used together in a turnaround document. A turnaround document is a document which :

• Has some information printed onto it by a computer.

• Has more information added to it by a human.

• Is fed back into a computer to transfer the added information into the computer.

Here is a turnaround document that a gas company could use to record meter readings.

The document is printed by a computer. The name, address and customer number of the person that the meter reader should visit is printed on the form. The customer's last meter reading is also included.

The meter reader takes the document and visits the customer's house. He then marks the current meter reading onto the OMR grid on the form. In the example the meter reader has marked the reading as 4605. The form is then returned to the gas company.

At the gas company the form is fed into a special reader. Optical character recognition is used to read the customer's number from the form. Optical mark recognition is used to read the meter reading that has been added. All of the information can be read into the computer automatically. A bill can be produced and posted to the customer without any need for human intervention. Turnaround documents allow cheap, fast input of information into a computer system

The turnaround document does not contain any instructions because the meter reader who fills it in will complete hundreds of similar forms every day. He will have been trained to use the forms so printing instructions on them would simply waste space.

Data can also be printed on turnaround documents in barcode format.

Alternatives to Turnaround Documents

In some industries turnaround documents are being replaced by small handheld computers. For example many gas companies now issue their meter readers with handheld computers. At the start of the day the names and addresses of the customers that the meter reader must visit are downloaded into the computer. As the meter reader visits customers' homes, he types the meter readings into the computer. At the end of the day the readings can be transferred automatically onto the main computer to issue bills. Handheld computers used to enter data into a computer system are known as Portable Data Entry Terminals (PDET).

4.26. Input Devices : Summary

Manual Input Devices
Input Device	Example Use	Advantage	Disadvantage
QWERTY Keyboard	Word processing.	Typists can use with ease to enter any textual data.	Relatively slow.
Concept Keyboard	Children's toys, tills in restaurants / pubs.	Can be operated by novices or people who can not manage a normal keyboard.	Needs to be customised for each application.
Touch Screen	Information system in tourist office window.	Can be used where a mouse or keyboard might get wet or dirty.	Tiring to keep touching screen.
Light Pen	Drawing on screen.	Cheap to manufacture.	Extremely inaccurate and awkward to use.
Mouse	Moving a pointer on screen.	Easy for novices to use for drawing or to choose options off the screen.	Requires a lot of space to use.
Tracker Ball	Moving a pointer on screen.	Does not need as much space as a mouse.	Not as intuitive to use as a mouse.
Touch Pad	Moving a pointer on screen.	Does not need as much space as a mouse.	Not as intuitive to use as a mouse.
Joystick	Playing games or controlling robots.	Allows fast, natural directional interaction needed for games.	Not as accurate as a mouse for selecting options from screen.
Graphics Tablet	Producing technical drawings.	Allows digitising of images with great accuracy.	Expensive unless you use it a lot.
Scanner	Transferring printed images onto a computer.	Cheap and fast method of getting graphics into a computer.	Images take up a lot of storage space.
Digital Camera	Including photographs in newsletters and DTP work.	No film required, no delay getting negatives processed.	Camera can only store a limited number of images, resolution is usually not very good.
Video Capture	Reads still or moving video images into computer. e.g. Video Digitiser, Webcam.	Can capture moving images.	Captured video files require a lot of storage space.
Voice Recognition (Microphone)	Telephone banking, automatic dictation.	Can be operated by inexperience users, can be used remotely by telephone.	Can only understand a few words or one person.
MIDI	Input and output of music via instruments.	Quicker and easier than entering music through computer keyboard.	Instruments and computer require MIDI ports.
Remote Control	Operating a TV from remote location.	More convenient than having to move to TV to operate it.	Can be lost, some controls do not work all functions of device.
Biometric Devices	Security applications where a person must be identified by fingerprint/iris e.g. passport.	More reliable identification than password, signature etc.	People are worried about personal data stored about them being misused.
Sensors	Control systems.	Many types available, automatic input of physical quantities.	May require calibration.
Direct Data Entry (DDE) Devices
Input Device	Example Use	Advantage	Disadvantage
Barcodes	Supermarket stock control.	Quick and easy to enter data under non-ideal condition, cheap to print bar-codes.	Only numbers can be stored in bar-codes.
Magentic Ink Character Recognition	Reading information from cheques.	Very fast and secure : numbers can not be changed by overwriting and not damaged by folding.	Expensive to buy reader and ink.
Magnetic Stripe Codes	Used to store a small amount of information on the back of credit cards	Simple and cheap to produce.	Can be damaged by magnetic fields or scratching.
Smart Cards	Petrol station points cards, satellite TV decoder cards, debit cards.	Can store a lot of information.	People worried about what information could be stored.
Optical Mark Recognition	Marking exam scripts, lottery tickets.	Fast and accurate.	Instructions have to be followed exactly by person marking the form.
Optical Character Recognition	Used to read printed text into the computer, reading postcodes to sort letters.	Fast method of reading text into a computer.	Not 100% accurate, OCRed documents must be checked manually.

5.	A turnaround document is a document which : Has some information printed onto it by a computer. Has more information added to it by a human. Is fed back into a computer to transfer the added information into the computer.
6.	A Portable Data Entry Terminal (PDET) is a handheld computer that can be used to enter data into a computer system as an alternative to a turnaround document.

5.1. Output Devices : Introduction

Once an information system has processed the inputs it receives it must present the results of the processing for the user.

An output device takes data from the computer and converts this into information in a form which is normally understandable by humans.

There are many different output devices available. Each output device is suitable for a different purpose. Select an output device from the table below to find out about it or read through the rest of this topic to learn more about all of the different output devices.

Soft Copy Output Devices
Monitors / VDUs
Hard Copy Output Devices
Printers	Dot Matrix
	Laser
	Ink Jet
	Thermal
Plotters	Flatbed
	Drum
Other Output Devices
Sound	Speakers
	MIDI
Microfilm (COM)
Control Devices

5.2. Output Devices : Monitor / VDU

Almost all computers have a monitor. Monitors are also known as Visual Display Units (VDUs). Most computers use this display as the main output device. There are two different types of display :

• Desktop Monitors (CRTs) : These work in much the same way as a television set. They are bulky but fairly cheap to buy. e.g. £60 for a 15" screen. Unlike LCDs desktop monitors can be viewed from many different angles.
  


• Liquid Crystal Displays (LCDs) : These displays are completely flat and consume very little electrical power so can be used in laptop computers and other small devices such as digital cameras. They are more expensive to make than desktop monitors and prices range from about £200 for a 15" display to £3,500 for a 40" display. As well as being much more compact than a standard desktop monitor, liquid crystal displays are flicker-free and can be used safely for much longer periods.

The two most important features of a screen are its size and its resolution. There is more information about these features below. They apply to both desktop monitors and LCDs.

• Size : How big is the screen ? Typical sizes are 15", 17" or 21". The size is measured along the diagonal from the bottom left hand corner to the top right hand corner of the screen.

• Resolution : An image displayed on the screen is made up of lots of tiny dots called pixels. If you look closely at the screen you may be able to see these pixels. The resolution of the screen is how many pixels there are up and down and from left to right across the screen. A variety of different resolutions are available. For PCs these resolutions have names. e.g. VGA is 640 x 480. This means that there are 640 pixels in each row across the screen and 480 pixels in each column up and down the screen.

The most common current resolutions are XGA (1024 x 768) and SXGA (1280 x 1024). Displays with lots of pixels are called high resolution. Displays with fewer pixels are called low resolution. High resolution displays can show much more detail than low resolution ones and are required for applications such as Computer Aided Design (CAD) and Multimedia. Here are close-up pictures of a circle, one shown on a high resolution display and one on a low resolution display :

Images displayed on the screen are temporary, i.e. they do not last forever. For this reason they are called soft copy.

5.3. Output Devices : Printers & Plotters

People often prefer to get printouts of the work they have done rather than to look at it on a monitor. Printouts are called hard copy. Unlike images on a screen hard copy can provide a permanent record of work and can be looked at away from the computer. Hard copy can be obtained using a printer or a plotter. There are lots of different types of printers and plotters available. They vary in the method they use to produce hard copy and the cost and the quality of the hard copy they produce. Different devices are suitable for different applications.

The main types of plotters and printers are listed here :

Printers	Dot Matrix
	Laser
	Ink Jet
	Thermal
Plotters	Flatbed
	Drum

A dot matrix printer is known as an impact printer because it makes an image on the page by hitting a hammer against a ribbon. Printers which do not do this are known as non-impact printers.

5.4. Output Devices : Dot Matrix Printers

Dot matrix printers are impact printers. They produce an image by hammering a column of 9 or 24 pins against a ribbon. Characters are produced as the print head (which contains the pins) moves across the page.

Dot matrix printers are cheap to purchase and have low operating costs. Most can run in either draft mode (quick but very low quality) or Near Letter Quality mode (slower but better quality). If carbon paper is put into the printer then a dot matrix printer can print more than one copy of a document at a time. This feature is often used by companies when they print invoices, bills etc. The company can keep one copy themselves and send the other copy to the customer. Dot matrix printers typically print at speeds around 300 characters per second (cps).

The disadvantages of dot matrix printers are that the output quality is poor, it takes a long time to print a document and the noise can be annoying.

5.5. Output Devices : Laser Printers

Laser printers are called page printers because they print a whole page at a time. A laser beam is used to draw the image to be printed onto a light sensitive drum. After the image has been drawn on the drum a fine powder ink called toner is put onto it. The toner only sticks where the laser has drawn the image. The paper then passes over the drum and the toner is transferred onto the paper.

Laser printers produce very high quality output, are very quiet and very fast. Typical home laser printers can print 16 pages per minute (ppm). Some industrial versions print over 100ppm and can print on both sides of a piece of paper at the same time. The main disadvantage of this type of printer is the high purchase cost. Small laser printers cost from £80 to buy and are more usually about £600. Colour laser printers cost £500+. Running costs are higher than dot matrix printers but lower than most ink jet printers.

5.6. Output Devices : Ink Jet Printers

Ink jet printers are the most popular type of printer for use at home or in a small business. This is because they are relatively cheap to purchase and can print in colour. Ink jet printers generate output by squirting tiny jets of ink at the paper to be printed on. A column of ink jets in the print head moves across the page squirting dots onto the paper to make the image.

Typically ink jet printers can produce 1200 to 4800 dots per inch (dpi). Because these dots are made with liquid ink photographs usually look better when printed on an ink jet printer than on a laser printer printer, but the quality of printed text is not quite as good. Ink jet printers nearly always print in colour and cost from £30 upwards. They are slower than laser printers (8 pages per minute+) and cost more to run as the ink cartridges they use are expensive.

5.7. Output Devices : Thermal Printers

Thermal printers are no longer used as printers for microcomputers. They are however still used in some computer control systems, tills and in many fax machines. These printers print on special heat sensitive paper which is relatively expensive. The image is produced from small black dots which are made on the paper by heating it up. The quality is reasonable and graphics can be printed. Documents printed on a thermal printer usually fade over time.

5.8. Output Devices : Plotters

A plotter can be used to produce very large drawings on paper sizes up to A0 (16 times as big as A4). A plotter draws onto the paper using very fine pens. There are two types of plotter. They differ in the way that the pen can be moved about on the piece of paper to draw lines :

• Flatbed Plotter : The paper is fixed and the pen moves left and right and up and down across the paper to draw lines.

• Drum Plotter : The pen moves up and down on the paper and the paper is moved left and right by rotating a drum on which the paper is placed.

Plotters can automatically change their pens and so can produce colour output. The lines drawn by a plotter are continuous and very accurate. Plotters are very slow but produce high quality output. They are usually used for Computer Aided Design (CAD) and Computer Aided Manufacturing (CAM) applications such as printing out plans for houses or car parts. The quality of the output produced by ink jet printers is now very good and large format (big) ink jet printers are steadily replacing plotters for most tasks.

5.9. Output Devices : Sound

Sound can be output through loudspeakers or headphones. On microcomputers you also need to install a sound card to be able to output sound. If you want you can connect the computer to a hi-fi to get louder, better quality sound than you would if you plugged the loudspeakers straight into the computer. The sound produced by microcomputers is now better quality than sound that is recorded on a CD.

Sometimes a computer can read out text that has been entered into it by using a computerised or recorded voice. This type of system is known as speech synthesis.

5.10. Output Devices : MIDI

The Musical Instrument Digital Interface (MIDI) system allows a musical instrument to communicate with a computer system. The musical instrument can act as an output or input device. As it is played computer software records information about the duration, pitch and volume of each note.

Music input into a computer by a MIDI instrument can be saved or edited by the user. It can also be printed out as a musical score. The computer can play the recorded piece of music either through its own speakers or through a MIDI instrument that is being used as an output device.

Sophisticated MIDI software can receive inputs from up to sixteen musical instruments at once and can play music back on many instruments simultaneously. The various instruments can all be sequenced together so that they play back in time with each other.

5.11. Output Devices : Microfilm

Microfilm is a special type of photographic film which can store images at greatly reduced sizes (about 1/50th of the original size). Traditionally companies that needed to store a lot of documents would photograph the documents and store the images on microfilm. The original documents would then be destroyed and the microfilm photographs of the documents would be kept instead. The microfilm photographs were much smaller than the original documents so they could be stored more efficently and cheaply.

Images stored on microfilm can be viewed using a special reader that magnifies the images and projects them onto a screen. Suitable readers are fairly cheap to buy.

Computers can output information directly to microfilm for long-term storage. This is known as Computer Output on Microfilm (COM).

Microfilm is rarely used today. Documents which need to be stored are usually scanned and saved electronically on high capacity storage media. Documents stored electronically can be indexed and searched more efficiently than documents stored photographically on microfilm.

5.12. Output Devices : Control Devices

Computers can also be used to control other devices such as motors and lights which can be switched on and off. These devices are activated by electrical signals sent to them by a computer.

There are lots of different devices available. Examples of common devices include :

The action of many devices will depend upon how high or low the analogue voltage that is sent to the device is. For example :

• A motor will rotate more quickly if it is supplied with a high voltage than if it is supplied with a low voltage.
• A bulb will glow more brightly if it is supplied with a high voltage than if it is supplied with a low voltage.

Devices like these are used by computerised control systems.

Computer Assisted Manufacturing (CAM) systems can control devices such as CNC lathes and robots and use these to make items.

5.13. Output Devices : Summary

1.	An output device takes data from the computer and converts this into information in a form which is normally understandable by humans.
2.	Soft copy output devices produce temporary output, whereas hard copy output devices produce permanent output.
3.	There are two types of Visual Display Unit (VDU). They are desktop monitors which use a cathode ray tube like a television and liquid crystal displays. Important factors when selecting a VDU are size, resolution and cost.
4.	Printers or plotters are hard copy output devices. Printers are either impact printers (produce output by striking a ribbon) or non-impact printers.
5.	The table below compares the main types of printers and plotters. Comparisons of Printers and Plotters Type Cost Speed Quality Graphics Paper Colour Fonts Dot Matrix £100 + 300 cps Poor Yes Continuous or Sheets Poor Lots with Software Laser £80-£15000 Mainly £600 8-100 ppm Excellent Yes Sheets Very Expensive Lots Ink Jet £30+ 8-24 ppm Excellent Yes Sheets Yes Lots Thermal Built into other devices (cheap). 3 ppm Poor Yes Roll of Special Paper No Lots Plotter £700-£5000+ Very Slow Excellent Yes Large Sheets e.g. A4-A0 Yes Draw as Graphics Abbreviations : PPM = pages per minute, CPS = characters per second
6.	Speakers can produce sound output such as music or synthesised speech.
7.	MIDI instruments can be controlled by a computer. Music can be played back through up to 16 instruments simultaneously.
8.	Microfilm is a special type of photographic film which can store images at greatly reduced sizes (about 1/50th of the original size). In the past documents were stored on microfilm but it is rarely used now.
9.	MIDI instruments can be controlled by a computer. Music can be played back through up to 16 instruments simultaneously.
10.	A wide variety of control devices such as motors, lights and pumps can be switched on and off by a computer.

6.1. Storage : Introduction

All information systems need to store data. This may be done temporarily whilst inputs are processed to produce outputs or for much longer periods of time.

For example :

• A school uses a database package to keep a record of the achievements of its students. These records are kept for the seven year period that each student attends the school.
• A student is using a graphics package to draw a logo on the screen. The graphics package must store the colour of each pixel in the logo so that it can be printed.

A computerised information system must be able to store both programs (e.g. a word processing package) and data (e.g. a word processed letter).

A storage device stores programs and data either temporarily or permanently. All information systems contain two different types of storage :

Immediate Access Store (IAS)	Immediate access store holds programs and data that the user is currently working with.
Backing Store	Backing store keeps data and programs when the computer is turned off.

Immediate access store is also known as main store or primary store. Backing store is also known as secondary store.

The capacity (amount of data) that a storage device can hold varies significantly between different devices. Units such as bytes, kilobytes and megabytes are used to describe a storage device's capacity. Other factors such as speed of data access, cost and portability will also determine which storage device is the most appropriate one to use for a particular application.

Select a storage device from the table below to find out about it or read through the rest of this topic to learn more about all of the different storage devices.

Immediate Access Store
RAM
ROM
Backing Store
Magnetic Disks		Floppy Disk
		Hard Disk
		Zip Disk
		Jaz Disk
Optical Disks		CD-ROM
		CD-R
		CD-RW
		DVD-ROM
		DVD-RAM
Magnetic Tape
Flash Memory Devices

6.2. Storage : Device Capacity

Various units of measurement exist to describe the capacity of storage devices. The smallest unit of storage is the bit. A computer can only store data as binary numbers (0s and 1s). A bit of storage can hold either a 0 or a 1. Devices such as computers which can only use binary information are described as digital devices.

Eight bits are grouped together to form a byte. Using 8 bits it is possible to represent any character on the keyboard with a byte. The characters are represented in 0s and 1s using a code called the ASCII code. Here are some example codes :

To store the sentence "Hello World" in a computer would require 11 bytes (one for each character), which is 11*8 = 88 bits.

Describing the capacity of a storage device in bytes would be silly. A typical home microcomputer can store 536870912 bytes in its immediate access store and 128849018880 bytes in its main backing store (probably a hard disk). Therefore there are a number of other related units that are used :

Typical Storage Capacity of a Microcomputer

A typical new home microcomputer has 512Mb of immediate access store. This is equivalent to :

• 512*1024 = 524288 Kb
• 512*1024*1024 = 536870912 bytes
• 512/1024 = 0.5Gb

The same computer is likely to have three backing storage devices, a floppy disk drive (capacity 1.44Mb), a CD/DVD drive (capacity 650Mb-18Gb) and a hard disk drive (capacity 120Gb+).

6.3. Storage : Immediate Access Store

Immediate Access Store ( IAS ) holds programs and data that the user is currently working with. For example :

• A word processed document that is being edited will be loaded into IAS.
• An email program that is currently transmitting a message will be loaded into IAS.

There are two different types of IAS :

• Read Only Memory (ROM) : The contents of ROM is permanent. It can not be altered by the user. The content is written onto the ROM when it is first made. ROM keeps its contents even when the computer is turned off and so is known as non-volatile memory. On some computers a special piece of software called the BIOS which is used to configure the computer is stored in ROM. ROM is also often used in embedded systems where a small built-in computer is used to control a device such as a washing machine. The program that controls the machine is stored on ROM.

• Random Access Memory ( RAM ) : RAM is used to store programs and data that are being used by the computer. When the computer is turned on the RAM is empty. Data and programs can be put into RAM from either an input device or backing store. The data in RAM is lost when the computer is turned off so it is known as volatile memory. To keep data the user must save it to backing store before the computer is turned off.

  • The process of transfering data/programs from backing store into RAM so they can be used is known as loading.
  • The process of transfering data/programs from RAM to backing store so that they will be retained when a computer is turned off is known as saving.

  It is easy to add extra RAM to a microcomputer by inserting extra RAM cards called SIMM or DIMM cards :

  

IAS is located inside the computer. Data can be written to and read from IAS electronically at very high speeds, much faster that it can be written to or from backing store. IAS is much more expensive to buy per Mb than backing store is.

6.4. Storage : Backing Store

If data needs to be kept whilst a computer is turned off then it must be stored on backing store. Any programs or data that are not currently being used by a computer will be kept on backing store. When programs or data are used they are copied (loaded) into immediate access store for faster access.

Information stored on backing store is placed on a storage medium. The most common media which are used for backing store are :

• Magnetic Disks

• Magnetic Tapes

• Optical Disks such as CD-ROMs and DVDs

• Flash Memory Devices

The data is read from or written to the storage medium by a piece of hardware known as a drive or a storage device.

It takes much longer to access data which is on backing store than data which is in immediate access store, typically 100 to 1000 times as long. This is because most backing storage devices operate mechanically. Computers have much more backing store than immediate access store for two reasons :

1. IAS only needs to store programs and data that are currently being used whereas the backing store needs to hold all of the programs and data that can be used on the computer.

2. Backing store is much cheaper per Mb than IAS.

Programs and data can not be used directly from backing store. They must be copied (loaded) into immediate access store before they can be used. Any data which needs to be kept must be transferred back to the backing store from the immediate access store before the computer is switched off. This is called saving.

Sometimes data is compressed before it is stored. Compressing data reduces the storage space that a file uses without losing any of its contents.

6.5. Storage : Magnetic Disks

Magnetic disks are the most common backing storage device. Data is stored using magnetised spots called domains on the disk. Each domain can store one bit of data (a 0 or a 1). A 3.5" 1.44Mb floppy disk used on a PC contains 16,777,216 such spots. A 3.5" 120Gb hard disk drive contains over 120 billion spots!

Data stored on disks is arranged along a series of concentric rings called tracks. Each track is divided up into a number of sectors. Data is read to and written from a disk one sector at a time. A sector usually contains 512 or 1024 bytes of data.

The process of dividing a disk up into tracks and sectors so it can be used on a computer is known as formatting. You must format a new disk before you can use it.

Data is read from the disk using a disk head which moves mechanically about the disk (rather like a record player tone arm). The disk head can move directly to any sector on the disk. Because of this a computer system can load a file or a record from a file very quickly. The system can move directly to the location of the record/file and read it without having to read any other data from the disk. This is known as direct access. For most applications using a direct access medium is much faster than using a serial access medium.

The two main types of magnetic disks are floppy disks and hard disks.

6.6. Storage : Floppy Disks

Floppy disks are magnetic disks. They are portable (can be moved between computers) but have a small storage capacity. Reading and writing data from a floppy disk is very slow. The most common type of floppy disk is the 3.5" disk that can store 1.44Mb of data when it is used on a PC. Older disks were 5.25" or 8" in size but could store much less data.

A floppy disk is manufactured from a flexible plastic disk. This disk is coated with a magnetisable material. For protection the disk is encased in a plastic shell. All sizes of floppy disk have a write protect tab built into the shell. If this tab is set then data can be read from the disk but not written to it. The write protect tab can be used as a security measure to prevent important data being deleted or changed accidentally.

Floppy disks are used for three main purposes :

Some hardware companies now produce storage devices which are very similar to floppy disks but can store 100Mb or even 750Mb of data. These devices are also much faster than standard floppy disk drives. An example is the Zip disk.

6.7. Storage : Hard Disks

Hard disks are magentic disks. They have much larger storage capacities than floppy disks. Data can be transferred to and from a hard disk much more quickly than from a floppy disk. Hard disks are usually fixed inside a computer and can not be moved between different machines. Some expensive hard disks can be moved between computers. These are called exchangeable hard drives. An example of this is the Jaz drive.

A hard disk is made of a rigid disk which is coated with a magnetisable material. The magnetic material used is of a much higher quality than that found on floppy disks. Hard disks spin much more quickly than floppy disks and the disk head is positioned very close to the disk (thousandths of a millimetre away). Because the disk head is positioned so close to the disk hard drives can easily be damaged by dust or vibration. Therefore the disk, the drive head and all the electronics needed to operate the drive are built together into a sealed unit. This picture shows a hard disk drive with the case removed.

Usually (as in the picture above) several physical disks are contained in one hard disk unit. Each disk is known as a platter. Typical hard disk capacities for a home PC now start at 80Gb and units storing up to 300Gb are available. If larger storage capacities are required then multiple hard drives can be combined. Using appropriate hardware or software many hard disks can be made to look like one very large hard disc to the user.

6.8. Storage : Zip and Jaz

Zip and Jaz disks are examples of removable magnetic disks. They can be used to transfer data from one computer to another, to backup data, or as an alternative to a hard disk for storing files.

6.9. Storage : Optical Disks

Optical disks store data by changing the reflective properties of a plastic disk. Binary computer data (0s and 1s) are represented by the way the disk reflects light when a low power laser is shone at it. A 0 stored on a disk reflects light differently to a 1 stored on a disk.

Like floppy disks, optical disks can be moved from one computer to another. They have much larger storage capacities than floppy disks but can not store as much data as a hard disk. Data can be read from an optical disk more quickly than from a floppy disk but hard disks are much quicker. As with a hard disk the drive head in an optical drive can move directly to any file on the disk so optical disks are direct access.

There are five types of optical disks that are currently in use. They are all the same physical size. It is possible to purchase a Combo drive that can read and write most of these different types of disks.

The five types of optical disk are :

CD-ROM (Compact Disk - Read Only Memory)

CD-R (Compact Disc - Recordable)

CD-RW (Compact Disc - Rewriteable)

DVD-ROM (Digital Versatile Disk - Read Only Memory)

Because of their high capacity, DVD-ROM disks are used to store high quality video such as complete movies. Often extra data such as information about the making of the film or the actors and actresses who star in it are also stored on the disk. Unlike movies recorded on video tape, DVD-ROM movies can be interactive. The user can make selections on the screen and change what they see.

DVD-RAM (Digital Versatile Disk - Random Access Memory)

DVD-RAM disks have all of the benefits of DVD-ROM disks and can be written to as well. These very high capacity disks are ideal for producing backups. They are starting to replace video tapes for recording television programmes. DVD-RAM disks typically store about 5Gb of data.

6.10. Storage : Magnetic Tapes

Magnetic tape comes in two different forms :

The storage capacities of tape cartridges are now so great that reels of tape are not used in new computer systems.

A computer tape is divided up into many blocks. A block on a tape is like a sector on a disk. To read data from a particular block on the tape all of the blocks that come before it must be read first. This means that finding a particular file/record on a tape can take much longer than finding a particular file/record on a disk. However once the file or record has been located it can be read more quickly from a tape than in could be from a hard disk. Having to read through all of the files/records that are stored before the file/record you want to access is known as serial access.

Often files or records are stored on a tape in a particular order (e.g. sorted alphabetically by a key field). If this is the case then the tape is described as having sequential access. Because locating data on a tape takes a long time, magnetic tapes are not used as general purpose storage devices. They are only useful for a few applications. The two main applications tape is used for are :

Applications for Magnetic Tapes
Backup	Often a tape streamer is used to make copies of data stored on a hard disk in case the data becomes corrupted. If this happens then the correct data can be restored from the tape. A backup copy of the contents of the hard disk could be made once every week. Tapes are more suitable for making backups than floppy disks or CD-ROMs. This is because the entire contents of a hard disk can be written onto one tape, producing the backup will be much quicker and tapes are cheaper to buy. It does not matter that tapes are serial access because when a backup is made or restored every file on the tape has to be accessed.
Batch Processing	In a batch processing system when processing occurs the whole master file and the whole transaction file are read to produce a new master file. Because the master file and transaction file are both sorted into the same order the data can be read sequentially from each file. A batch processing system does not have to move backwards and forwards through a tape looking for records. The system is designed so that the next record to be read is stored immediately after the current record on the tape. Therefore using a serial access medium instead of a direct access medium will not slow down processing. Tapes are preferred to disks in batch processing systems due to their relative low costs and fast read/write speeds.

6.11. Storage : Flash Memory

Flash Memory devices store data electronically in a type of memory that can have data written to it and (unlike RAM) can retain the data when the power to the memory is turned off. Commonly flash memory devices store data in Flash Erasable Programmable Read Only Memory (FEPROM).

Several different types of flash memory device are available. These include Compact Flash, SmartMedia, Secure Digital and USB Pen Drives.

Flash memory devices are very compact, most being a similar size to a postage stamp or coin. For this reason they are often used as backing storage in small devices such as digital cameras and PDAs. Typical storage capacities are from 32Mb up to about 2Gb. The cost per Mb of flash memory storage is high compared to other backing storage devices.

6.12. Storage : Disk Cache

Accessing data stored permanently in backing store is much slower than accessing data in RAM. A common technique that is used to speed up access to data on backing storage devices is caching.

A cache is a part of a computer's RAM that is set aside to store copies of frequently used sectors on a backing storage device such as a hard disk drive. As files are accessed from the hard disk the computer will determine which sectors of the disk are being used most frequently. Copies of the data that is located in these sectors are transferred into the cache.

After this whenever the data in these sectors is read or changed the computer will use the copies of the sectors in the cache rather than the original sectors on the disk. Since the cache is located in RAM these accesses will be many times quicker, so the operation of the computer system will be speeded up.

The contents of the cache are lost when the computer is turned off. This is because cache is located in RAM which is volatile. To ensure that any changes made to sectors in the cache are saved permanently to the hard disk drive the computer system will copy these sectors back to the hard disk drive at a time when the drive is not being used or when the computer is properly shut down.

6.13. Storage : Access Methods

There are three different methods which can be used to access (locate) data stored on a backing storage device. They are direct access, serial access and sequential access.

Direct Access

When direct access is used the head that reads data from the storage medium can move directly to any point on the storage medium. If a particular record or file must be loaded or saved then the head can move directly to the record/file's position on the storage medium and read the data. Records and files can therefore be located very quickly.

Magnetic disks such as hard disks and floppy disks and optical disks such as CD-ROMs use the direct access method. Direct Access is required if transaction processing is taking place.

Serial Access

When a serial access medium is being used, the head that reads data from the storage medium has limited freedom of movement. The only serial access medium is magnetic tape.

To read a particular record/file from a serial access medium, all of the data that comes before the record/file must be scanned through. The tape head can not move to a particular record/file on the tape without reading through all of the other records that come before it.

Because of this it can take a very long time to locate a record/file on a tape and so tapes are only used for specific applications such as backup and batch processing. For these applications the speed of locating data is not important and the other advantages of magnetic tapes outweigh the slow access speed.

Sequential Access

Sequential access is a slight modification of the serial access method. This method is identical to serial access except that the records are stored on the storage medium in a particular order, e.g. by customer number. Sorting the data into an order may speed up operations such as searching the tape. The sequential access method is usually used by batch processing systems.

6.14. Storage : Compression

When data is stored it occupies space on a storage device such as a hard disk or floppy disk. Buying storage space costs money. To reduce the cost of storing data users often attempt to reduce the size of the files they want to store without losing any of the data.

Data compression is the act of reducing the size of a file without losing any of the data it contains. Decompression (also known as uncompression or expansion) is the act of taking a compressed file and converting it back to its original size and format. Because compression alters the format of the data in a file a compressed file must be decompressed before it can be used.

How much a file can be compressed by will depend upon the method being used to compress the file and the data that is stored in the file.

The three most common applications for which data compression is used are :

• Distributing Software
• Hard Disk Compression
• Data Transmission

Distributing Software

Software is often distributed on CD-ROMs. The software must be installed onto a hard disk before it can be used. Software manufacturers usually compress the files that make up a package on the CD-ROM. When the software is installed onto a hard disk the files are decompressed by the installation software.

Hard Disk Compression

Files stored on hard disks can also be compressed. Some utilites will compress and decompress individual files whilst others can compress an entire hard disk automatically as files are saved and loaded.

Compressed files may load more quickly or more slowly than files that are not compressed. This will depend upon how well compressed a file is and the speed of different components of your computer hardware.

Data Transmission

Compression is also used when data is transmitted over a telephone line. Modems will only allow the transmission of data at very slow speeds (e.g. 3Kb per second). To transmit a picture the size of an A4 page can take over ten minutes. If data that is to be transmitted can be compressed before it is sent then there can be considerable advantages :

There are a variety of agreed standards for compressing data that is sent over telephone lines. Some modem manufacturers claim compression ratios of 1:4 (i.e. data can be reduced to a quarter of its original size before being transmitted). Such high compression rates are rarely achieved.

6.15. Storage : File Processing

Two common methods of processing saved files are sorting and merging. These are often used by batch processing systems which store data as records in files. For example a file might contain records about people who are employed by a company. There would be one record per employee.

Sorting

Sorting is arranging the records in a file into a particular order, such as by employee number.

Merging

Merging is combining the contents of two files into one file. The simplest method of merging two files together is to just take the contents of one file and add them to the end of the other. This is known as appending :

If the records in a file must be kept in a particular order (a sequential file) then the merge process is more complex. To carry out a merge the algorithm shown in this flowchart must be followed :

The results of the merge are also shown in the above diagram. Note that unlike a simple append, this more sophisticated merge has produced a new file that maintains the required order. The records in two files that are to be merged must have the same record structure.

6.16. Storage Devices : Summary

1.	Computerised information systems have to store programs and data.
2.	A storage device stores programs and data either temporarily or permanently.
3.	The capacity of a storage device is described in terms of bits, bytes, kilobytes, megabytes and gigabytes. Unit Equivalent To 1 Bit A single storage location which can hold either a 0 or a 1. 1 Byte 8 Bits 1 Kilobyte (Kb) 1024 Bytes 1 Megabyte (Mb) 1024 Kilobytes 1 Gigabyte (Gb) 1024 Megabytes
4.	There are two different types of storage device : Immediate access store holds programs and data that the user is currently working with. Backing store keeps data and programs when the computer is turned off.
5.	Immediate access store is also known as main store or primary store. Backing store is also known as secondary store.
6.	Immediate access store can be either ROM or RAM : Read Only Memory (ROM) : Contents are kept when computer is turned off (non-volatile) but can not be altered. Random Access Memory (RAM) : Contents are lost when computer is turned off (volatile) and can be altered by the user.
7.	ROM is used to store the BIOS program in a microcomputer and the programs that run embedded systems. RAM is used to store programs and data the user is currently working with.
8.	There are many different types of backing storage device. The main ones are : Types of Backing Storage Device Type Examples Common Applications Magnetic Disk Floppy Disk Transporting files, small backups. Hard Disk Running software, storing data files. Zip/Jaz Transporting big files, medium size backups. Optical Disk CD-ROM Distributing software, multimedia products. CD-R Permanent backups, small volume distribution. CD-RW Temporary backups. DVD-ROM High quality digital films. DVD-RAM Backup of moderate volumes of data. Magnetic Tape High volume backups, batch processing. Flash Memory Transferring files, storage in compact devices.
9.	To select an appropriate storage device for a task several different criteria should be considered : What the maximum storage capacity of the device is. How much the device costs per megabyte (Mb) of storage space. How quickly the data stored on the device can be accessed. Whether the device can store data whilst the computer is turned off. Whether the data stored on the device can be changed or not. Whether the storage device can be used to transfer data from one computer to another or not (is it portable?). The method used to store the data e.g. electronically, magnetically, optically.
11.	The table below compares the main types of storage device. Device Capacity Cost per Mb Transfer Speed (capacity per second) Direct or Serial Access Stores Data when Computer Switched Off Can Have Data Written to It Portable Immediate Access Store RAM 32Mb to 1024Mb 35p 500Mb to 1500Mb Direct No Yes No ROM 1Kb to 64Mb 35p 500Mb to 1500Mb Direct Yes No No Backing Store Floppy Disk 1.44Mb 17p 0.2Mb Direct Yes Yes Yes Hard Disk 40Gb to 300Gb 0.05p 40Mb to 100Mb Direct Yes Yes No Zip / Jaz 100Mb to 2Gb 1p 0.5Mb to 8Mb Direct Yes Yes Yes Optical Disk 650Mb to 17Gb 0.02p 3Mb to 22Mb Direct Yes Depends on Type Yes Magnetic Tape 20Gb to 400Gb 0.03p 5Mb to 60Mb Serial Yes Yes Yes Flash Memory 16Mb to 1024Mb 20p 0.4Mb to 10Mb Direct Yes Yes Yes
12.	Caching is a technique used to speed up access to data stored on a backing storage device. A cache is a part of a computer's RAM that is set aside to store copies of frequently used sectors on a backing storage device such as a hard disk drive so that they can be accessed more quickly.
13.	Backing storage devices can be accessed using one of three access methods : Direct Access : The drive head can move directly to any record/file on the device so locating data is very fast. All types of disk are direct access. Used for transaction processing. Serial Access : The drive head must read through all of the data that comes before the record/file to be loaded so locating data is slow. Only magnetic tapes are serial access. Used for batch processing. Sequential Access : Identical to serial access, but records/files are stored in a particular order.
14.	Data can be compressed before it is stored so that it will use up less storage space.
15.	Compression is the act of reducing the size of a file without losing any of the data it contains. Decompression is the act of returning a compressed file to its original size and format. A file that has been compressed must be decompressed before it can be used.
16.	How much a file size is reduced by when it is compressed will depend upon the type of data that is stored in the file and the method used to compress the file. Important applications of compression are distributing software, hard disk compression and data transmission.
17.	Common file processing techniques include sorting and merging : Sorting is arranging the records in a file into a particular order. Merging is combining the contents of two files into one file. The simplest method of merging two files together is to take the contents of one file and add them to the end of the other. This is known as appending.

7.1. Processing : Introduction

Processing is the act of doing something (e.g. organising and manipulating) with data to produce output. Processing is at the centre of our model of an information system :

There are three distinct methods of processing data : batch, transaction and real-time processing. In a computerised information system most of the processing is carried out by a hardware device known as a microprocessor.

7.2. Processing : The Microprocessor

The microprocessor is the hardware device that processes data. The microprocessor contains electronic circuitry which can :

• Perform mathematical calculations on data.
• Make decisions using data.
• Handle control signals from devices such as keyboards and hard disks that require the processor to do something.
• Move data from one part of the computer to another.

Most personal computers (known as microcomputers) contain just one microprocessor. Minicomputers and mainframe computers may contain many microprocessors. All of the microprocessors that are contained in one computer are known as the computer's Central Processing Unit or C.P.U. A computer that contains more than one microprocessor is able to carry out more than one task at the same time and is described as being capable of parallel processing.

7.3. Processing : Batch Processing

Using batch processing input data is grouped together into batches . No data is processed until a complete batch has been collected. Then all of the data in a batch is processed in one go. There may be a long time delay between data being input into the system and the data being processed.

In this type of system the important data that the computer stores all of the time is kept in a file called the master file. The data in the master file is sorted into order using one of the fields in the records in the file, known as the primary key field. The primary key field must uniquely identify each record in the file.

Each piece of input data (which will update the contents of the master file) is known as a transaction. All the input data is put together into a batch in a file called the transaction file. There are three different types of transaction that any processing system will have to cope with. They are :

• Add a new record to the master file.
• Delete a record from the master file.
• Amend / update an existing record in the master file.

At some predetermined time (e.g. the end of the day or week) the computer system will process the data stored in the transaction file and make any changes that are necessary to the master file as a result of the transactions. This will produce an updated master file and an error report detailing any transactions that could not be processed for some reason. Generating a single updated master file from the old master file and the transaction file is known as merging files.

Before this processing can take place the transactions must be prepared for processing. To do this two operations must be carried out :

1. Validating : Each transaction that is entered is validated to check that it is unlikely to halt processing by causing an error. It is very important that processing is not halted in a batch processing system because processing often takes place overnight without a human operator being present. If an invalid transaction caused the processing to stop then a whole night's processing time could be lost. Transactions are usually validated as they are keyed in by the operator. Any errors that are found can be reported and corrected straight away.

2. Sorting : The data in the transaction file is sorted into order using the same primary key field as the master file. Sorting can not take place until the whole batch of transactions entered and stored in a file. The transaction and master files need to be put into the same order before processing occurs because the two files are processed sequentially. The files are usually stored on a serial access medium such as magnetic tapes. If the records on the tapes were not sorted into order then whenever a transaction record was read from the transaction file the computer system would have to waste a lot of time searching for the matching record in the master file.

How often batches of data are processed will depend upon the application (i.e. the job that is being done). Batch processing is usually only carried out on mainframe computers and when very large volumes of data have to be processed in a database.

This system flowchart shows what happens in a batch processing system :

Batch Processing Algorithm

During the processing phase (represented in the bottom half of the flowchart above) all of the records are copied from the master file to the new master file. Any changes that must be made to the master file are detailed in the transaction file and carried out when the records are copied to the new master file. The processing that takes place for each transaction in the transaction file will depend upon the type of transaction :

There is nothing to stop a batch processing system being implemented using disks for storage rather than magnetic tapes. Tapes are usually used because they are cheaper to purchase, can store more data and can read and write data faster than disks.

7.4. Processing : Payroll System

Payroll systems are often implemented using batch processing :

• The master file would contain the records for all of a company's employees, including their employee number, rates of pay and how much they have been paid so far this year. The records in the master file would be sorted using the employee number as the primary key field.

• The input data put into the transaction file would consist of records showing how many hours each employee had worked in the current week. Sometimes transactions would be used to add a new record if a new employee started or delete a record when an employee left the company.

Here is an example record for an employee called Anna Jones in a master file together with an entry in the transaction file which will update her record with the number of hours she has worked this week.

After the transaction file was processed, Anna's record in the master file would show that her pay so far this year was £5762.50. This would include the £187.50 (25 hours at £7.50) she had just earned.

The transaction file would be processed at the end of each week as workers are paid weekly. Before processing it would have to be sorted into the same order as the master file, i.e. the records would be sorted into order by employee number.

The computer would then process the transactions, using the information about how many hours each employee has worked this week (from the transaction file) and their rates of pay (from the master file) to calculate the employee's wages for the week. Payslips can then be printed and the master file can be updated to increase the amount paid so far this year by the wages paid this week. An error report will also be produced.

This system flowchart shows the operation of the payroll system :

7.5. Processing : Transaction Processing

For some applications the master file needs to be kept up to date all of the time. For example in a travel agents whenever a seat is booked on a flight the number of seats that remain available on the flight must be reduced by one immediately. If this update was not done until the end of a day (as might happen in a batch processing system) then the flight could become overbooked with the same seat being booked more than once.

Transaction processing systems are used whenever the master file must be kept up to date. A transaction processing system operates like this :

• When a transaction is entered it is placed in a queue of transactions waiting to be carried out. The transactions are processed in the order that they are placed into the queue. If there are many people using the system at the same time then there could be lots of transactions being made from different computer terminals.

• The computer system will process one transaction at a time. Once the system starts processing a transaction it will not process any other transactions until the current transaction is finished. When a transaction is processed the master file is updated immediately. Therefore the master file is always kept up to date.

Under normal circumstances a well designed transaction processing systems will process a transaction within a few seconds of the transaction being inputted. During peak processing times (e.g. Saturday morning in a travel company) the time that it takes for a transaction to be processed will increase. For most systems this is acceptable. When it is not acceptable, a real time processing system must be used instead.

Transaction processing systems need to use direct access files. In a direct access file any record in the file can be updated directly, without having to read through all of the records that come before it in the file. Serial access media such as magnetic tape can not be used. The time required to find the record in the master file that a transaction related to would make processing incredibly slow.

Transaction processing is interactive, i.e. processing takes place as a "conversation" between the user and the computer : The computer responds to the user’s input by outputting some data before the user can input any more data. This means that the user's input can depend on the computer's previous output.

Transaction Processing is also known as Interactive, On-Line or Pseudo Real Time Processing.

7.6. Processing : Point of Sale Stock Control System

A supermarket uses a Point of Sale (POS) terminal to keep track of the goods that it has in stock and to produce bills for customers. Whenever an item is sold the product code of the item is read into a till by a barcode scanner. Sometimes the barcode is not scanned properly. If this happens the product code must be rescanned or entered using a keyboard.

Once the product code has been entered the till looks up the price and name of the product in the supermarket's stock database. This information is printed on the customer's receipt. It also updates the product's record in the stock file to indicate that the product has been sold.

This system can be depicted by this system flowchart :

The system has to be a transaction processing system because a customer at a till would not be prepared to wait for a batch processing system to look up the price and name of the product. It is not worth spending a lot more money to purchase a real time system to carry out this task because small delays at peak times can be tolerated.

7.7. Processing : Real Time Processing

For some tasks a computer must process information to meet some real world time deadline. The time deadline must be met regardless of how much work the computer has to do. Usually real time computer systems are required to process information very quickly. Most real time systems appear to process data instantly.

A computer system which must process data extremely quickly to meet a real world deadline is known as a real time system.

For example, consider a control system that is used to fly a guided missile to hit a target. Once the missile is launched the control system must guide it to its target. The missile's guidance system identifies its position by examining the contours / features of the ground it is flying over. This input data is used to ensure that the missile follows the path it has been programmed with. Using the inputs the system will decide how to move ailerons/fins to change direction and control the speed of the rocket motor.

Because a missile flies very fast the inputs must be processed very quickly to affect the outputs. If it took two seconds for the missile to change its direction to avoid an unexpected object then the missile would probably hit the object before the change of direction could take place. The data must be processed in thousandths of a second to avoid a disaster. There is a real world time limit on how long the computer system can take to process data without having terrible consequences. Therefore a missile control system has to be a real time system.

Most real time systems are control systems. Other examples include the cooling system in a nuclear reactor which prevents the reactor overheating or any system which must control a dangerous chemical reaction.

Real time systems are very fast but they do not process data instantly. Any processing will take some time. However real time systems will process data very quickly. To ensure that any input data can be processed sufficiently quickly real time systems must incorporate a lot of redundancy. This means having much more hardware than is required to process the expected amount of input data. The extra hardware is known as redundant hardware because it is not normally used. Under normal circumstances only a small fraction of the hardware is required. In extreme circumstances when there is an unusually large amount of input data to process the redundant hardware can be used. Therefore the system will not slow down and will still be capable of meeting deadlines.

Redundant hardware can also be used as backup hardware to reduce the likelihood of a computer system failing if some of its hardware fails.

Having to incorporate lots of redundant hardware makes real time systems very expensive. They are usually only used in safety critical situations.

7.8. Processing : Summary

Comparison of Processing Methods
Comparison	Batch	Transaction	Real Time
Identifying Features	Input data is collected into batches in a transaction file which is sorted and validated before being processed with the old master file to produce a new master file.	The master file is always kept up to date. Transactions are placed in a transaction queue and processed in the order that they are added to the queue.	Data is processed extremely quickly to meet a real world deadline.
Example Applications	1. Payroll 2. Printing Bills 3. Multiple Choice Exams	1. Ticket Booking 2. Seat Booking 3. Stock Control 4. Banking	1. Missile Guidance 2. Nuclear Reactors 3. Chemical Processes
Speed of Response	No data is processed until a complete batch is collected. It may be a long time e.g. a day before data is processed.	Under normal loads data is processed within a few seconds. Under heavy loads processing times can be longer.	Data processed very quickly to meet a real world deadline. Processing often appears to be instant.
Storage Media Used	A serial access medium such as magnetic tape.	A direct access medium such as magentic disk.	Usually immediate access store.
Cost

8.1. Software : Introduction

A piece of software is a computer program which has been written to carry out a particular task. Without software the hardware that is used to build a computer system would not be very useful. A software program contains the instructions that the computer must follow to carry out a task. Sometimes more than one program is required to complete a task. When this is the case the group of programs which together complete the task are known as a software package.

Software programs are originally produced by computer programmers who will write the instructions that form the program in a programming language.

Example pieces of software are :

• A word processor.
• A multimedia encyclopaedia.
• A spreadsheet.

A piece of software is usually classified as being either systems software or applications software.

8.2. Software : Classification

A piece of software is usually classified as being either systems software or applications software.

Systems Software

Systems software controls the operation of a computer. Without systems software a computer would not function. The most important piece of systems software is the operating system. The operating system will perform vital tasks such as :

• Managing communications between computer and connected peripherals.
• Providing a user interface.
• Allocation of computer memory.
• Organising data on backing storage devices.

Other pieces of system software will perform less essential tasks such as backing up files. These programs are known as utilities. Example utility programs are :

• Disk Defragmenter : Reorganises files stored on a disk to speed up loading and storing files.
• Backup Software : Used to produce copies of information stored on a computer so that if data is lost it can be recovered.

Applications Software

Applications software is software that is written to solve a particular problem or carry out a particular job. Application software can be either generic or application specific.

(1) Generic (General Purpose) Software

A generic software package is a package that can be put to a wide variety of uses. For example a spreadsheet package can be used for any task involving calculations or graph plotting. The most common generic software packages are :

Word Processor	Used to produce simple documents such as letters and essays.
Desktop Publisher	Used to produce complicated documents such as leaflets, posters and newspapers.
Graphics Package	Used to produce pictures and diagrams.
Database	Used to store information so that it can be easily searched.
Spreadsheet	Used to perform calculations and draw graphs.

Some generic packages are described as being integrated packages. This means that they incorporate more than one program. For example an integrated package may include a word processor, spreadsheet and database. The individual programs in an integrated package are designed to work well with each other. Information can easily be transferred between each program. Additionally the user interface of each program will be similar so that if you have learnt how to use one program it will be relatively easy to learn how to use another.

(2) Application Specific Software

An application specific package is produced to perform one specific task. For example a program that was written to produce invoices and manage stock levels for a garage would be application specific software.

8.3. Software : Selecting Software

If you have a task to carry out on a computer you will need to choose the most appropriate software to use for the task. For example, is a spreadsheet or a database more suitable for keeping records of all of the members of a club ? Factors such as ease-of-use, speed, availability of software, your familiarity with the software, staff training, and the features of a software package will influence your choice.

The three important points you must cover when selecting software are :

• Identify the activities that you will need to carry out to tackle the problem.
• Investigate and explain how each of these activities could be carried out using two or three different methods.
• Draw a conclusion about which is the best method to use. Be sure to justify your conclusion.

If you have to select software for a project then one possible way of writing up your software selection is to draw up a table like this example.

Sometimes there is no software package available which will let you carry out the task properly. If this is the case then you must develop a completely new system.

8.4. Software : Selecting Software Example

In this example a student has to select an appropriate package to write up a science experiment. The write up must include text, a table of results and a graph showing the results.

Having considered the task I have identified a number of different activities that I will need to carry out to write the essay. I have also identified some other activities that would help me write the essay but are not essential. In order of importance these activities are :

1. Enter and output ordinary text.
2. Produce tidy tables.
3. Produce graphs.
4. Let me correct errors.
5. Check my spelling.
6. Let me use different typestyles to highlight titles.
7. Number the pages.

I have considered two possible methods of producing the essay. They are (i) using Microsoft® Notepad and (ii) using Microsoft® Works™. Both of these methods are available for me to use. In the table below I have explained how each of the activities can be carried out using each of the methods.

The best option is to use Microsoft Works. It will allow me to carry out all the tasks I want to. I can correct my text on screen before printing and Works will help me find my spelling mistakes - saving a lot of time. Tables can be easily created and edited in a range of attractive styles. The spreadsheet can be used to incorporate a graph. A number of different fonts can be used to make titles stand out. Works will also automatically number my pages for me.

Microsoft® Notepad and Microsoft® Works™ are trademarks and/or registered trademarks of Microsoft Corporation in the United States and other countries.

8.5. Software : Development

Usually if you want your computer to perform a particular job then you can go to a shop and purchase a software package that will do that job. Software packages that are readily available from shops are known as "off-the-shelf" packages.

Sometimes more than one package will be available which could perform the job you need to do. If this is the case then you will need to look at the features of the different packages to select the most appropriate package.

If no package exists that will do the job you need then there are two options available to you :

8.6. Software : Summary

1.	A piece of software is a computer program which has been written to carry out a particular task.
2.	Software programs are originally produced in a programming language.
3.	Software is usually classified as being either systems software or application software.
4.	Systems software controls the operation of a computer. The operating system and utility programs are systems software.
5.	Application software is software that is written to solve a particular problem or carry out a particular job. Application software can be either generic or application specific : Generic A generic package is a package that can be put to a wide variety of uses. The most common generic software packages are : word processors, desktop publishers, graphics packages, spreadsheets and databases. Application Specific An application specific package is produced to perform one specific task. For example a program written to produce invoices and manage stock levels for a garage.
6.	If you need a piece of software that will perform a specific task then you will have to choose from one of three options : Off-the-shelf : If a package already exists that performs exactly the task that you need then you can buy it "off-the-shelf" from a shop. Customise a Generic Software Package : Modify a generic package such as a database to carry out the task. Custom Written Software : Pay a computer programmer to write a new piece of software to perform the task.
7.	To select a piece of software for a particular job it is useful to draw up a set of comparison criteria, based upon what you need the software to do.

9.1. Word Processing : Introduction

A word processing package is used to prepare and edit text. Word processors are used to create all types of documents such as letters, reports and essays. Using a word processor you can type, revise and correct a document on the screen before printing it out. The layout of the page can be changed and a wide variety of different styles of text can be used to improve the presentation of a document. Tools such as spelling checkers can help ensure that the contents of a document is accurate.

The functions of a word processor can be divided up into several different categories :

Page Layout	The page layout functions let you decide how each page will be set out.
Text Presentation	The appearance of text can be easily altered. Different fonts and styles can be used and the size of text can be varied. Text can be neatly lined up on the page.
Editing of Text	Text editing functions are used to revise and change text that you have entered.
Blocks of Text	The style and position of selected blocks of text can be changed.
Text Analysis	The word processor can look at your document and try to highlight any errors such as spelling or grammatical mistakes that you have made.
Templates	Template files let you save favourite document layouts that you have created so that you can use them over and over again.
Other Features	Most modern word processors will offer lots of extra features such as tables, bullet points and fancy text effects.
Mail Merging	A database of names and addresses can be used to personalise letters that have been created in a word processor.

A word processor is not always the best package to use to produce a document. Sometimes you may require more control over the layout of a page or you may wish to include a lot of graphics in a document. If this is the case then a Desktop Publishing (DTP) package would be more suitable. Desktop Publishers are often used to produce newspapers and books. As extra features are added to word processors it is becoming increasingly difficult to distinguish between a word processor and a desktop publisher.

9.2. Word Processing : Page Layout

Size

Computer printers will let you print word processed documents on several different sizes of paper. Most printers can use Letter and A4 size paper. Bigger printers will also print on A3 paper. Letter size paper is the standard in America and A4 is the standard in Europe.

It is important that the word processor is set to use the correct size of paper for your printer. This will ensure that all of your text will fit onto the page and that there will not be a large unused gap around the edge of the page.

Orientation

You can print onto a piece of paper in one of two orientations, which are usually known as portrait and landscape. These two orientations look like this :

Sometimes portrait is known as tall and landscape is known as wide.

Margins

It is usual to leave a small gap between the writing on a page and the edge of the page. This gap is called a margin. Leaving a margin is especially important when you need to bind a document together. Even if you do not want to leave a margin you will probably have to. Most printers can not print right to the edge of the page. 

You can normally set the size of the top, bottom, left and right margins separately by typing in the distance from the edge of the page to the text.

Headers and Footers

When writing a document containing many pages such as a report you may want the same information to appear at the top and bottom of each page. For example you may want the name of the document and your name to appear at the top of each page. You may want to print each page's number at the bottom of the pages.

• Header : Text appearing at the top of each page is known as a header.
• Footer : Text appearing at the bottom of each page is known as a footer.

Many word processors will let you type special codes which will automatically insert information such as the current date or current page number into the header or footer of a document.

Columns

A page can be divided up into a number of columns. This is particularly useful if you want to produce a newspaper, newsletter or a leaflet which will be folded.

9.3. Word Processing : Text Presentation

The text presentation functions let you specify what printed text will look like and how it will be positioned on the page.

Fonts

A font is a style of writing. Modern word processors are supplied with a wide range of fonts for you to choose from. Different fonts are useful for different purposes. Plain fonts such as Arial and Times New Roman are good for writing letters and reports. Fancier fonts such as Keystroke and Lincoln are suitable for use on posters.

Font Size

Most fonts are scalable. This means that you can use them at any size you want. The size a font appears at is specified by a number known as the font size. Sizes 10 and 12 are the most common for writing letters and reports. Fonts sizes are specified in 1/72ths of an inch. So fonts at size 72 are one inch tall and fonts at size 36 are half an inch tall. Larger fonts can be used for headings, posters etc.

Font Style

Each font can have a range of extra styles applied to it. The six common styles are :

• Normal : No special style is applied to the font.
• Italic : The font will be displayed as if it is leaning slightly to the right.
• Bold : The lines used to draw the font will be drawn extra thick to make the text stand out.
• Underline : A line will be drawn underneath the text.
• Superscript : The text is raised up to the top of the line and printed at a smaller size.
• Subscript : The text is lowered to just below the line and printed at a smaller size.

Alignment

Alignment describes the position at which text appears on a line on the page. Alignment is sometimes known as justification. There are four different type of alignment :

• Left Alignment : Text is lined up with the left hand edge of the page.This is the default alignment in most word processors.
• Right Alignmnent : Text is lined up with the right hand edge of the page. This is mainly used to put addresses onto letters.
• Center Alignment : Text is placed on the middle of the line. This is often used for headings.
• Full Justification : Text is automatically spread out so that it is lined up with both the left and right hand edges of the page. This form of layout is often used in newspapers.

Indentation

Text on the first line of a paragraph is often indented a short distance from the left hand margin. The first line of this paragraph has been indented :

9.4. Word Processing : Editing Text

One of the biggest advantages of using a word processor over preparing text manually is entered text can be easily edited. This means that mistakes can be corrected without spoiling the presentation of the final document. There are three main methods that you can use to edit text :

• Deleting and Retyping : The simplest way to edit text is to delete any incorrect text using the backspace or delete keys and then retype the correct text in its place.
• Copy / Cut and Paste : The copy and paste function can be used to duplicate text that has already been typed in. Cut and paste can be used to move a block of text from one position in a document to another.
• Search and Replace : The search and replace function will look through the document to find a word that the user specifies. When the word is found the computer can automatically replace it with another word that the user types in.

9.5. Word Processing : Blocks of Text

Many word processor functions can be applied to selected blocks of text. A block of text can be selected by using a mouse or the cursor keys. The selected text is usually highlighted by the word processor. When a block of text has been highlighted its properties can be changed. For example :

• The font, style and size can be changed.
• The alignment of the text can be changed.
• Cut or copy and paste can be used to move or duplicate the text.
• The block of text can be deleted.

9.6. Word Processing : Text Analysis

Word processors provide tools which will check the text that you have typed and highlight and possibly correct any errors that it contains. Almost all word processors will include a spelling checker. More sophisticated packages also include thesaurus dictionaries and grammar checkers.

Spell Check

A spelling checker will examine the text that you have typed and identify any spelling mistakes. When a mistake is found most spelling checkers will attempt to "guess" what the correct word should be and make some suggestions to you. You can accept one of the suggestions or retype the word correctly yourself.

Spelling checkers have quite large dictionaries, typically 80,000 words. However there will be some words that are not in the dictionary such as peoples' names. You can usually add extra words to the dictionary that is supplied with the word processor.

A spelling checker can not spot mistakes where you have typed the wrong word, e.g. it will not spot "their" instead of "there" or "the" instead of "they".

Thesaurus and Grammar Check

Advanced word processors may also offer thesaurus or grammar check features :

• A thesaurus will suggest alternative words with the same meaning as a word that you have typed in. Such words are known as synonyms. For example if you type "big" the thesaurus might suggest "large", "huge" and "vast".
• A grammar checker will examine the structure of any text you have typed. It may highlight some grammatical errors or give you a score to indicate how good your grammar is. The grammar checkers that are available at the moment are not very good.

9.7. Word Processing : Templates

When you have designed a document layout that you like you may want to use it again for other documents in the future. For example :

• A company may want to set out all the letters it sends in a particular way. The letters may always include a logo and the company's address at a particular position on the page. The same font may be used for the text on each letter.
• A student may want to present all her essays in the same way. The essay title and the student's name could appear at the top of each page and the page number could appear at the bottom of each page. A standard font could be used for the main text and a different font could be used for each heading.

If you have designed a document layout that you want to reuse then you can save it as a template file. When you start a new document you should load the template file to begin with. The template file will contain all the layout information for the new document. Using templates can ensure that the appearance of the documents you produce is consistent. It can also improve your productivity as you do not have to recreate the layout you want every time you start a new document.

Word processors are often supplied with a variety of templates for common tasks such as letter writing, reports and producing curriculum vitaes.

9.8. Word Processing : Other Features

Most modern word processors will include lots of extra features in addition to those described above. Some common "extras" include :

• Tables : Many word processors contain a special tool that will let you create tables and format them as you want. If a word processor does not contain a table tool then you can use tab stops and the tab key to line tables up neatly. Using the tab key like this is known as tabulation.
• Bullet Points and Numbering : If you want to present a list of points then many word processors will automatically add bullet points before each item in the list or number the points.

9.9. Word Processing : Mail Merging

Mail merging is a technique used mainly by companies and clubs to send personalised letters to customers or members. Using a standard (or form) letter and a database of names and addresses personalised letters addressed to the people in the database can be easily produced. The names and addresses of the people are automatically put onto the letters :

There are four main steps that must be followed to create mail merged letters. They are :

• Create The Database : If the database containing the names and addresses of the people to send the letter to does not already exist then it must be created.
• Link The Letter And Database : The database and letter must now be linked together so that the mail merge function knows which file contains the names and addresses to fill into the letters
• Write The Letter : The letter to send should be created in the word processor. Special codes must be placed in the letter where the names and addresses of the customers should appear.
• Perform The Mail Merge : When the mail merge is performed one letter will be produced for each person in the database. The names and addresses will be filled in on each letter.

Companies believe that personalising letters in this way will increase the probability that customers will respond to advertisements. The customer is fooled into believing that the company has sent an advert specifically to him. In fact many thousands of people could receive the same letter.

Selective Mail Merges

Mail merged letters can be sent to every person whose name is recorded in a database. Alternatively a query can be used to select only some of the people in a database to send the letter to. For example :

• A company that is trying to market conservatories would not want to waste money sending letters to people who live in flats which have no garden. A query could be used to select only the people who live in houses from a database of names so that money is not wasted sending advertisements to people who could not possibly want a conservatory.
• A club could use a query to select the names of people who need to renew their membership from a database of members. Mail merged reminder letters could then be sent to these people.

When letters are sent to only some of the people in a database this is a selective mail merge. Selective mail merges are much more useful than simple mail merges which produce letters for everyone in a database. If you intend to use a database to carry out a selective mail merge then you must register the database with the Data Protection Commissioner to comply with the Data Protection Act.

9.10. Word Processing : Summary

1.	A word processing package is used to prepare and edit text.
2.	The most important features of a word processor package are listed in this table.

Page Layout
Orientation	Which way round the paper is printed on (portrait or landscape).
Margins	The gaps between the text and the edge of the page.
Header and Footer	Text which appears at the top and bottom of each page.
Columns	Pages can be divided into columns for producing leaflets, newsletters etc.
Text Styles
Fonts	Different styles of text.
Font Size	Text can be printed at many different sizes.
Font Style	Styles such as bold, underline and italic can be applied to text.
Alignment	Text can be lined up on the left, right or center of the page or be fully justified.
Editing Text
Copy / Cut and Paste	Blocks of text can be duplicated or moved using the copy, cut and paste options.
Search and Replace	A word or phrase can be automatically replaced with another wherever it occurs.
Text Analysis
Spell Check	The spelling in a document can be automatically checked and corrections suggested.
Thesaurus	A thesaurus will suggest alternative words with the same meaning as a word that you have typed in.
Grammar Checker	A grammar checker will examine the structure of any text you have typed.
Templates
Templates	Templates let you store favourite document layouts to reuse.
Other Features
Tables	Tables can be used to set data out neatly in rows and columns.
Bullets & Numbering	Bullets and numbers can be used to present lists of data.

10.1. Desktop Publishing : Introduction

Desktop Publishing (DTP) software is used to produce professional-looking documents such as reports, books, posters or leaflets. DTP software gives you more control over the layout of a page than a word processor and lets you easily integrate graphics into your publications. In addition to the features of a word processor you should also expect a desktop publisher to offer you these facilities :

Page Layout	The ability to define the layout of a page using frames to place text and pictures in.
Fonts and Styles	A wide range of fonts and styles.
Drawing Tools	Some drawing facilities, although these may be limited.
Importing Pictures and Text	The ability to incorporate pictures and text from other packages in a document.
Clipart	A library of pictures for you to include in your documents.
Accurate Positioning	The ability to position objects extremely accurately on the page using guidelines or a grid.

Many desktop publishers include wizards. A wizard is an interactive tool that guides the user through a potentially complex task. Using a wizard lets the user complete a common task more quickly and straightforwardly than starting from scratch.

10.2. Desktop Publishing : Page Layout

A page in a desktop published document is set out as a group of frames which are positioned onto the page by the user. Here is an example page layout for the front page of a newsletter :

This layout includes two text frames which will contain the article that is to appear on this page. There is one picture frame which will contain a photograph to illustrate the article. The top frame will contain a header which will appear on every page in the newsletter. A frame can usually contain either text or a picture (but not both). A frame can be positioned and resized independently of all of the other frames.

This diagram shows the layout of all of the pages in the newsletter :

Although the exact layout of each page is not the same, the designers of the newsletter have adopted a consistent design for each page, i.e. :

• The same header at the top of each page.
• Two columns on each page.

The page designers will also have chosen consistent font styles so that text on each page has a standard appearance.

Linking Frames

Often an article on a page will not fit into one text frame. An article may have to be split between two or more text frames which may or may not be on the same page. So that this can happen desktop publishing packages will let you link frames together. You can link any number of frames together in any order to form a chain. When one text frame is filled up the text in the frame will automatically flow into the next text frame in the chain.

This diagram shows how the newsletter frames will be linked together :

The facilities to draw frames anywhere on a page and link them together in any order make a desktop publisher a far more powerful package for setting out documents than a word processor.

10.3. Desktop Publishing : Fonts And Styles

A desktop publisher should provide a wider range of fonts and styles than a word processor would. For example many DTP packages incorporate a "fancy" text function. This function may let you :

• Make text follow unusual paths such as a wavy line or an uphill slope.
• Add shadows to text.
• Use a range of colours and blends of colours to display text.
• Resize text by simply stretching the frame it appears in with the mouse rather than typing a font size.

The text below was created using the fancy text feature of a DTP package.

10.4. Desktop Publishing : Drawing Tools

All desktop publishers incorporate some drawing facilities. Some will include most of the features of a drawing package. Others will have much more limited facilities. As a minimum most DTP packages will let you :

• Draw straight lines.
• Draw simple shapes such as rectangles, squares and circles.
• Colour in lines and shapes.
• Create borders around text and picture frames.

If the drawing features of your desktop publisher are not very good then you may find it easier to produce any drawings in a graphics package and then import the results into the DTP program.

10.5. Desktop Publishing : Importing

Desktop publishing packages will let you assemble work from a variety of other packages into one document. For example :

• Text stories can be written in a word processor.
• Illustrations can be produced in a graphics package.
• Charts and tables can be produced in a spreadsheet.

The work produced in each of these packages can be brought into the desktop publisher which is used to lay out the information on the page as you want it to appear. A user may choose to produce work in another package rather than directly using a desktop publisher as the other package may offer better features than the desktop publisher. For example a spreadsheet will probably be capable of producing better charts than a DTP program could.

The process of bringing work produced in another package into a DTP program is known as importing.

Importing can be achieved by either copying and pasting data from one package to another or loading a file produced by another package into the desktop publisher. Desktop publishers will usually import files produced by a wide variety of other packages.

Sometimes special standard file formats such as Rich Text Format (RTF) or JPEG graphic file formats are useful. Most packages can output information in one of these common formats. All desktop publishers will be able to import information in these formats.

Hardware devices such as a scanner or a digital camera are often used to transfer pictures onto a computer for use in desktop published documents.

10.6. Desktop Publishing : Clipart

Clipart images are provided as libraries of pictures either with a desktop publishing package or separately. A clipart library will typically contain thousands of images relating to commonly used subjects. These images can be used within the desktop publisher to improve the appearance of work. Example categories might include :

• The Office
• Sport
• Leisure
• Transport

Clipart images can usually be resized and moved about on the page but can not usually be edited by the user. The use of clipart can greatly speed up the production of documents.

10.7. Desktop Publishing : Grids and Guidelines

To achieve a truly professional appearance it is important to be able to position objects such as text frames or pictures accurately onto the page. If a picture is placed above a text frame but they do not quite line up then the appearance of a document can be spoiled. Two tools are usually provided to help you position objects accurately. They are guidelines and grids.

Guidelines

Guidelines are lines which are placed onto the page to help the user position objects. The user can place guidelines anywhere on the page. Any object placed near to a guideline will "jump" or "snap" to the guideline. i.e. the object will move to line itself up exactly with the guideline. The guidelines will appear on the screen but will not appear on the final printed page.

Grids

A grid of points can be placed over a page. The points are placed at regular intervals specified by the user, for example every one centimetre. Whenever an object is placed on the page it will jump to the nearest point on the grid.

10.8. Desktop Publishing : Wizards

Many users of desktop publishing software want to carry out very similar tasks such as creating newsletters, posters, greetings cards and certificates. Completing these tasks from scratch can be very time consuming, so most desktop publishers include a wizard tool to allow common tasks to be complete more quickly and straightforwardly.

A wizard is an interactive tool that guides the user through a potentially complex task, such as creating a newsletter. The wizard will ask the user questions about the layout of the newsletter and create a basic document that matches the users requirements. The user can then edit the document manually to complete the creation process. The type of question that a newsletter wizard might ask include :

• What size paper will the newsletter be printed on (A4, A3 etc.) ?
• How many pages will the newsletter include ?
• How many columns of text on each page ?
• Which pages will have pictures on them, and how many ?
• What style should the newsletter have (formal, informal, modern, traditional, colourful etc.) ?

The questions asked by a wizard will depend upon what the wizard does. Other software packages such as databases and spreadsheets may also include wizards to help the user complete common tasks.

10.9. Desktop Publishing : Summary

1.	Desktop Publishing (DTP) software is used to produce professional-looking documents such as reports, books, posters or leaflets.
2.	A DTP package gives you much more control over the layout of pages in a document than a word processor would.
3.	In addition to the tools provided by a word processor, most DTP packages will provide the tools detailed in this table.
	Page Layout Pages are set out using text and picture frames. Text frames can be linked in any order to produce complicated layouts. Fonts and Styles Text can be made to follow unusual paths and be displayed with shadows and in a range of special effects. Drawing Tools Basic drawing tools such as lines, shapes and borders will be provided. Importing Pictures and Text Information produced in other packages such as a word processor, spreadsheet or graphics package can be put into documents created by a DTP package. Clipart A clipart gallery will contain thousands of useful pictures which can be incorporated into documents. Accurate Positioning Grids and guidelines can be used to position objects very accurately on the page.
4.	Many desktop publishers include wizards. A wizard is an interactive tool that guides the user through a potentially complex task. Using a wizard lets the user complete a common task more quickly and straightforwardly than starting from scratch.

11.1. Graphics : Introduction

Computer graphics or images are often used either by themselves or to enhance the quality of other documents, for example a desktop published document. There are three distinct types of package which can be used to create images on a computer. They are :

Painting Packages	This is the most basic type of graphics package. These packages allow you to paint onto the screen as if it was a canvas. Unfortunately they produce files which take up a lot of storage space and painted images are difficult to edit.
Drawing / Vector Drawing Packages	These are more sophisticated than painting packages. They store images as a set of objects which can be easily edited.
Computer Aided Design (CAD) Packages	Very advanced, highly accurate packages which can be used for designing three dimensional objects such as houses and machinery.

Many special hardware devices are available to help in the production of computer graphics. These include :

• Scanners and digital cameras which can transfer real-world images into the computer.
• Graphics tablets which can be used to accurately transfer drawings of objects into a computer.
• Large high-resolution monitors which allow detailed work to be carried out on large images.
• Plotters and high-quality computer printers for obtaining accurate output on paper.

11.2. Graphics : Painting Packages

Painting packages allow you to paint onto the screen as if it was a canvas. Many tools will be provided to help you do this. The most common tools are :

Painting packages are the best type of package to use if you want to edit scanned images such as photographs.

Painting packages store images as a series of small dots called pixels. If you zoom far enough into the image you will be able to see the individual pixels. The colour of each individual pixel on the screen must be remembered and saved. Files storing the colours of each pixel in an image are known as bitmap files. Because so much information has to be stored files saved by painting packages are usually very large. An image the size of a typical computer screen (800*600 pixels) would take up over one megabyte of memory. Therefore images produced by painting packages are often stored in a special compressed format such as GIF or JPEG.

Painting packages have one major limitation. It is the same limitation that you will find if you try to paint a picture on canvas. This limitation is that once a mark has been placed onto an image it is extremely difficult to change it. The only way to erase a mark is to paint over it in the same colour(s) as the background. There is no simple way to move a mark from one position in an image to another. Most packages provide an undo feature so that you can erase one unwanted mark immediately after you have made it. But in general it is very difficult to edit an image with a painting package.

A further limitation of images produced by a painting package is that if you enlarge them too much then you will be able to see the individual pixels that make up the image. The image will look very blocky or pixelated.

11.3. Graphics : Drawing Packages

Drawing packages overcome many of the limitations of painting packages. They make it easier to edit images and can store images in much smaller files. Images produced this way do not look blocky (pixelated) if enlarged. Drawing packages are also known as vector drawing packages.

Drawing packages do not store images by remembering the colour of each pixel in the image. Instead an image in a drawing package is built up from a number of shapes or objects. The drawing package remembers the position, size, shape and colour of each object that you place onto the image.

For example this image :

would be stored as a definition similar to this one :

1. Image Size = 220 * 120
2. Rectangle size 200,100 at location (10,10). Outline only, outline colour blue.
3. Circle radius 40 at location (150,60). Outline colour black, fill colour red.
4. Straight line from (10,10) to (150,60). Line colour green, thickness 5.
5. Text "Hi!" at location (25,80). Text size 14, colour black, font name Arial.

Basic Features of a Drawing Package

Because a drawing package remembers all of the information about each object you can easily change the appearance of the objects and hence the image.

A drawing package will provide these extra editing features :

A drawing package will also offer all of the tools that a painting packages does with the exception of a freehand brush and flood fill which will not be available.

Layering Objects

Objects stored as part of a drawing are stored in layers on top of each other. In the example image above, the layer that the green line is stored in must be on top of the layer that the red circle appears in because the line is in front of the circle. Drawing packages usually provide functions to move objects between layers.

Grouping Objects

Several objects can be grouped together so that they can edited as if they were a single object. For example several objects may be used to build up an image of a car. These objects could then be grouped together. Once grouped together all of the objects in the car image could be stretched, copied and moved as if they were one single object.

Accurate Positioning of Objects

To achieve a professional appearance it is important to be able to position objects very accurately onto the page. Two tools are usually provided to help you position objects accurately. They are guidelines and grids.

11.4. Graphics : Computer Aided Design (CAD)

Computer Aided Design (CAD) packages are the most sophisticated computer graphics packages. They are used by architects to design buildings and engineers to design machinery. CAD packages operate in a very similar way to drawing packages. They store information about each object that makes up an image so that the image can be easily manipulated. A fully featured CAD package may cost several thousand pounds.

The most notable features that are present in a CAD package which are not present in a drawing package are :

Computer Aided Design programs can sometimes be connected directly to automatic machinery such as a lathe which is controlled by the computer. A design made on the program could then be manufactured automatically using the lathe. When a CAD program is used like this it is called Computer Assisted Manufacturing (or CAM).

11.5. Graphics : Summary

1.	There are three different types of computer graphics packages which can be used to produce images. They are painting packages, drawing packages and computer aided design (CAD) packages.
2.	Many specialist hardware devices such as scanners, digital cameras, high resolution monitors, plotters and printers are available to assist in the production of computer graphic images.
3.	This table compares the three different types of computer graphics packages.

Comparison of Graphics Packages
Comparison	Painting	Drawing	CAD
Image Storage Method	Images are made up of thousands of small dots called pixels. The colour of each pixel is stored in a file known as a bitmap. This makes image files very large and difficult to edit.	Two dimensional images are stored as groups of objects. This makes image files small and easy to edit.	Three dimensional images are stored as groups of objects. Images are easy to edit and can be viewed from any position.
Tools	1. Palette 2. Freehand Brush 3. Straight Lines 4. Shapes 5. Text 6. Flood Fill 7. Zoom	As for a painting package, but : 1. No Flood Fill 2. Probably No Freehand Brush Objects can be : 1. Moved 2. Resized 3. Deleted 4. Grouped 5. Accurately Positioned	As for a drawing package, but all tools will work with 3D objects and be more accurate. Many CAD packages can also : 1. Store Libraries of Components 2. Cost Designs 3. Control Computer Assisted Manufacturing (CAM) equipment
Advantages	1. Cheap to purchase. 2. Easy to use.	1. Easier to edit images. 2. Images can be resized without becoming jagged/pixelated. 3. Image file size is small.	1. Can produce 3D designs. 2. Many highly sophisticated tools for designers.
Disadvantages	1. Image files are very large. 2. Difficult to edit images. 3. Resizing images produces jagged/pixelated results.	1. Unlike a CAD package only works with 2D images .	1. Very expensive to purchase. 2. Training is required to make good used of a CAD package.
Cost

12.1. Databases : Introduction

A database is a computerised record-keeping system. Databases are used when a large quantity of information has to be stored. A database is very useful because it will provide tools to let the user search through the data that has been stored to find particular pieces of information. The data stored in the database must be organised so that the computer can analyse and search it automatically.

Data in a database is usually organised into one or more files storing information relevant to the organisation that has created the database. For example a database keeping information for a doctors surgery may contain the following files :

Each file is identified by a filename (e.g. "Patient", "Employees"). Sometimes a file in a database is known as a data table.

When setting up a database it is usual to define a set of queries which will be used to answer questions from the data in the database. The output that is produced by the database is called a report.

There are two different types of database package that you are likely to find in a school. They are flat file databases and relational databases.

12.2. Databases : File/Table Design

Data entered into a database is stored in files (also known as tables). A file is a collection of records, each of which contains information about one person or thing. The data in the records is separated into fields which each hold just one item of data. Each field is identified by a field name.

The following diagram shows examples of a file, records and fields that might be used in a doctors’ surgery to keep information about patients. There is a file containing information about all of the patients. Within this file there is one record for each patient.

To create a file you need to tell the computer the names of the fields that will be stored in the records in the file. All of the records in a file must contain the same fields. You will also have to specify what type of data can be stored in each field and how much space should be reserved to store the data. Together, this information is known as the structure of the record (see example).

You should know and understand these important database terms :

Remember that a flat file database can store just one file, whereas a relational database can store many files in one database.

12.3. Databases : Field Data Types

Each field in a record must have a type The field type refers to the kind of data that can be stored in the field. Possible field types include :

Only data that matches the type of a field can be stored in a field. For example you could not store the word "cricket" in a field which is set to be numeric. Some databases will also let you store images and sound recordings in fields.

12.4. Databases : Field Lengths

Each field in a record can be of either fixed or variable length. When you create a file you must decide whether each field will be of fixed or variable length :

If a field is of variable length then an End-Of-Field marker must be put after the data stored in the field to show where it ends.

If a record contains some fields which have variable lengths then the record length will be variable. If a record contains only fixed length fields the record length will be fixed.

The main advantages of variable over fixed length fields or records are:

• A variable length field can store an item no matter how long it is.
• There is less wastage of space. Each item of data is stored in a space just one character longer than the item of data (it is one longer since an end-of-field marker must follow the field).

The main advantages of fixed over variable length fields or records are :

• Allocation of storage space is simple - each field / record requires the same amount of space.
• Updating files is simpler - if a field is edited the new contents will be the same length as the old contents so can simply be stored back over the old contents.

12.5. Databases : Key Fields

Usually one particular field of each record contains an item which is used to identify the record. This field is called the key field . The value in the key field must uniquely identify each record.

A patient number could be used as a key field to uniquely identify each patient’s record in the doctors’ patient file. The patient’s name could not be a key field as there may be more than one patient with the same name.

Sometimes a record may contain more than one key field. For example the doctor’s patients file may contain both a patient number and a National Insurance number for each patient. Both of these are key fields. We therefore choose one of them and call it the primary key field.

Often records are stored in a file sorted into order using the primary key field. When records are stored in a file in a particular order we say that the file is a sequential file. This is especially likely to be the case if the files are stored on a serial access medium such as magnetic tape.

12.6. Databases : Coding

Sometimes information is coded before it is typed into a database. For example consider a library database where books are classified as being fiction, non-fiction or reference. This information could be stored in an alphabetic field of fixed length 11 ("non-fiction" is 11 characters long). Alternatively the classifications could be coded like this :

• Fiction coded as F
• Non-fiction coded as N
• Reference coded as R

Using these codes the information can be stored in an alphabetic field of length one. Coding information reduces the amount of storage space required and speeds up the process of typing the information in. It also makes it easier to validate data as coded information must usually be in a specific format. For coding to work properly everyone needs to know what the correct codes are.

12.7. Databases : Relationships

If you are using a relational database then you will be able to create more than one file within a database and link the various files together. Links between different files in a database are known as relationships.

Here is an example showing the relationship between a Products File and a Suppliers File in a stock control database. The names of the fields in each file are shown in the example, but the record structure (data types, field lengths) is not.

The relationship between the files is made through the Supplier No field which appears in both files. The supplier of a particular product is identified by the Supplier No in the Products File. To find the details of this supplier (name, address etc.) this Supplier No can be looked up in the Suppliers File. Through the user creating a relationship between these two files the database software is able to automatically look up details related to the supplier of a product and to prevent the user accidentally entering a Supplier No in the Products File that does not match a supplier in the Suppliers File.

To create a link between two files the fields that are linked must have the same data type. It is also common for fields in a relationship to have the same name and for one of the fields in the relationship to be the primary key field in a file.

12.8. Databases : Library Example

A library database is being set up. The database will be created with a relational database package.

Identifying The Files

The database needs to store information about three different things. These are the library's members, books and the loans it has made. The database designer has therefore identified these three files that the system will require :

• The members file will store details of all of the people who can borrow books.
• The books file will store details of all of the books that the library owns.
• The loans file will store details of which members are currently borrowing which books.

File Structure

For each of the three files the designer must now decide what information the file should contain. This will include the field names, types and lengths. A primary key must also be identified for each file.

Members File

The members file will store information about each borrower. The primary key field must be Membership Number as it is the only field which will uniquely identify each person. Member Name can not be a key field as two borrowers could have the same name.

Books File

The books file will store information about each book the library owns. The primary key field must be Copy Number which can uniquely identify each copy of each book.

The category of each book, e.g. "History", "Geography", "Science Fiction" will be coded as a three letter code e.g. "HIS" or "GEO" to reduce storage space and speed up data entry.

Loans File

The loans file will store details of who has which books on loan at the moment. When a book is borrowed a record will be created in the loans file which will store the Membership Number of the borrower, the Copy Number of the book and the date the book is due back. Copy Number must be the primary key field. Membership Number can not be a key as a borrower may borrow more than one book at a time.

Relationships

The following relationships exist between the three files :

• The Membership Number in the Members File is linked to the Membership Number in the Loans File.
• The Copy Number in the Books File is linked to the Copy Number in the Loans File.

These relationships can be used to find out information using the data in the database. For example to find out who has the book "100 Facts about Animals" the database software must :

• Look up the Copy Number of the book in the Books File.
• Look up the found Copy Number in the Loans File to locate the Membership Number of the person who has the book on loan. If no record exists for the Copy Number in the loans file then the book is not on loan.
• Look up the found Membership Number in the Members File to find the name of the member who has the book.

12.9. Databases : Data Entry

When the database structure has been created you will want to put data into the files in your database. You may also want to change data that is stored in your database. There are three important operations that you may carry out on data in a database :

In a simple database package you will probably have to type the data directly into the files. More sophisticated database packages let you develop your own user interface through which data can be entered and manipulated. This is done by the creation of forms (or views) that let the user enter and view data simply. Here are two example forms that are part of a library system :

The buttons on the forms (Add, Cancel and Go) will cause the database to carry out specific actions when they are pressed. The user may be able to define these instructions with macros.

Sophisticated database packages will also let you specify rules that can be used to check data as it is entered. These rules can check that entered data is sensible but not that is correct. They are known as validation rules.

12.10. Databases : Validation

Sophisticated database packages can validate data that you enter into a database to ensure that it is sensible. Data can be validated as it is typed into a file or form. Validation checks on fields in a file are usually specified at the time that the file is created. Here are some common types of validation checks that can be carried out by database software :

Validation Checks
Presence Check	Checks that data has been entered into a field and that it has not been left blank. e.g. check that a surname is always entered into each record in a database of addresses.
Type Check	Checks that an entered value is of a particular type. e.g. check that age is numeric.
Length Check	Checks than an entered value e.g. surname is no longer than a set number of characters.
Range Check	Checks that an entered value falls within a particular range. For example the age of a person should be in the range 0 to 130 years.
Format Check	Checks that an entered value has a particular format. e.g. a new-style car registration number should consist of a letter followed by 1 to 3 numbers followed by 3 letters.
Table Lookup Check	Checks that an entered value is one of a pre-defined list of valid entries which should be allowed.

12.11. Databases : Queries

A query (also known as a filter or search) is used to answer a question from the data in a database. Queries look through the database and find all the records that match a particular condition (or criterion). They are normally defined in a very basic language called a query language. When a query is run it produces as output a list of all of the records that match the condition that defined the query. A common query language is called SQL which stands for Structured Query Language.

Recall the patients files in the doctors surgery database :

The following condition could be used to search this file to locate all of the patients who see Dr Jones :

Here are some other examples queries :

The comparisons that you can make in queries will depend upon the database program that is being used. Common ones are :

Reversing Queries

Sometimes you may want to search for records which do not match a particular criterion. For example you may want to find everyone who is not a patient of Doctor Jones. The keyword NOT is used to do this.

• Doctor = "Dr Jones" finds all the patients of Dr Jones.
• NOT Doctor = "Dr Jones" finds all the patients who do not see Dr Jones.

Queries Using More Then One Field

More complicated queries can be created by linking together more than one search condition. For example this condition can be used to find all of Dr Jones’ patients who have blood type O :

Blood Type = "O" AND Doctor = "Dr Jones"

This condition will find all of the patients who live in Hanley or were born after 1985 :

Address contains "Hanley" OR D-O-B >= 01/01/86

The words AND and OR are the only ones that can be used to link two simple conditions together to make a more complicated query. The difference between using AND or OR to join two conditions is :

• AND : Find only records which match both of the conditions.
• OR : Find records that match either or both of the conditions.

Using Brackets In Queries

For very complicated queries you may need to use brackets to tell the database what order to use to evaluate the conditions that make up the query. Brackets are used for the same purpose in mathematics :

e.g. (2*3)+4 does not give the same result as 2*(3+4)

The brackets tell the person doing the sum which order to use to calculate its different parts. Similarly when writing a query :

1. (Address contains "Hanley" OR Address contains "Stoke") AND D-O-B >= 01/01/86
2. Address contains "Hanley" OR (Address contains "Stoke" AND D-O-B >= 01/01/86)

would produce different results. Query (1) would find everyone who lives in either Hanley or Stoke who was born after 1985. Query (2) would find everyone who lives in Hanley (not just those born after 1985) as well as anyone who lives in Stoke who was born after 1985.

Queries Using More Than One File

So far all of the queries that we have looked at use data from one file only. With a flat file database this is not a limitation because flat file databases can only use one file at a time. However when working with relational databases this is a significant limitation. One of the important advantages of a relational database is that queries can be written which use data from more than one file. To enable this a much more sophisticated query language is required than the one we have used. SQL or Structured Query Language is one such language. The language must specify what data to look for and which file to look in.

Consider a database that stores information about which forms the students at a school are in. The database has two files. The first contains information about students and has the fields Student and Form. The second contains information about forms and has the fields Form and Form Tutor. Here is the contents of the two files :

Students File

Form Tutors File

To find out the names of all of the students in Mr J. Smith's form the database would have to :

1. Find out the name of Mr Smith's form (4LA) from the Form Tutors File.
2. Look in the Students File to see which students are in that form.

In SQL one way to express this query would be :

SELECT *
FROM [Students File], [Form Tutors File]
WHERE [Form Tutors File].[Form Tutor] = "Mr J. Smith" AND [Form Tutors File].Form = [Students File].Form

A detailed knowledge of a powerful query language such as SQL is not required for a GCSE course.

12.12. Databases : Reports

Often you may only want to display some fields from the records that are in your database or display the records in a particular order. A report defines how the records in a database (or those found by a query) will be displayed. Typically a report will let you specify these things :

• Which fields to display.
• Where to display the fields.
• The order in which records should be displayed.
• How records should be grouped together.
• What statistics you want the database to calculate from the records (e.g. no. of records, average values of fields).

Standard reports can be either tabular (set out as a table) or columnar (set out as a form). Alternatively a report designer can be used to define exactly how a report should be set out.

Tabular Reports

When a tabular report is printed multiple records are printed on each page. Each record takes up one line in a table. The names of the fields are printed at the top of the table.

Here is an example tabular report :

The report sorting options will determine in what order the names are printed on the report. Grouping could be used to divide the people on the report into groups. For example the patients could be put into groups by the name of the doctor they usually see. Most databases will print each group on a separate page.

Columnar Reports

Columnar reports print each record on a separate form. Usually each form is printed on a different page. Here is an example of a columnar report :

Columnar reports are often used for printing items such as tickets.

Report Designer

A report designer lets the user decide exactly how a report will appear. The designer works much like a desktop publisher. The user can use tools from a toolbox such as a text tool and drawing tools to define how the report will appear. Fields of information from the database can be positioned anywhere on the report.

Report designers can produce much more advanced reports than simple tabular or columnar reports. Some report designers can also perform calculations using the data in a report and even draw charts from the data.

12.13. Databases : Sorting

Most databases will let you sort data so that it is displayed in a particular order. To sort a database into an order you must specify :

• Which field in the database you wish to use to order the records. This will usually be the primary key field.
• Whether you want the records in ascending (going up) or descending (going down) order.

Sometimes you may wish to use more than one field to sort a database. For example if a database contained a list of names and addresses then you might choose to sort it by surname. However some people will have the same surname, so you may decide to tell the computer that if two people have the same surname they should be put in order by their forenames.

If you do this then the fields that you choose to use to sort the database are known as the 1st sort field, 2nd sort field and so on.

12.14. Databases : Macros

A macro is a short sequence of instructions that will automate a task. People who make databases often create macros to simplify the use of a database.

A macro in a database is a short sequence of instructions that the database will carry out. Writing a macro is like writing a program in a high level language. The user writes the instructions that will carry out the actions required of the macro. Common tasks that macros are used to perform in a database include opening and closing forms, printing reports and running queries.

Once a macro has been written it must be saved. The macro can then be executed (or run) whenever the user requires it. Often macros are associated with buttons on forms so that when a button is pressed a particular macro is excecuted.

12.15. Databases : Import and Export

Importing Existing Data

Sometimes the data that you want to store in a database is already available somewhere else such as in a another database, a spreadsheet or word processed document. If this is the case then instead of manually typing the data in again it will be quicker and easier to import it automatically from the existing source.

Before you can import data into a database you will need to save it in a standard file format such as a Comma Separated Value (CSV) or Tab Separated Value (TSV) file. The database package will then be able to read the data out of the file and store it within the database. You may need to create the record structure that will hold the data manually before importing the file or the database may be able to do this itself by analysing the imported data.

Exporting Data

Databases contain tools (such as queries) that let you analyse the data they contain. Sometimes however you may wish to take some data from a database and use it in another package. For example :

• You may wish to perform some calculations on data found by a query with a spreadsheet.
• You may wish to include a list of products stored in a file on a website.

To do this you must save the data that you wish to use in the other package in a standard file format such as a Comma Separated Value (CSV) or Tab Separated Value (TSV) that the other package can read. This is known as exporting data.

12.16. Databases : Relational vs Flat File

In a flat file database data can only be stored in one file. Here is an example of a flat file database that stores information about students in a school including what form they are in and who their form teacher is :

There are two serious problems that have been caused by trying to store this data in a flat file database :

• Redundant Data : Some data is stored more than once. This means that storage space is wasted and inconsistency can occur.
• Data Inconsistency : Because some items of data are stored more than once, it is possible that in error two different values for the same item could be stored.

Relational databases have two important advantages over flat file databases :

• Control Over Redundant Data : Wherever possible data is only stored once, so storage space is not wasted
• Data Consistency : Because each data item is stored only once it is not possible for the same item to store two different values, hence the data will always be consistent.

12.17. Databases : Designing a Database

You should follow these ten steps to help you design a database :

12.18. Databases : Testing a Database

What To Test

After you have created a database you need to test it to ensure that it is working properly. There are three main areas that you need to test. They are :

1.	Test that the database will accept reasonable inputs and (if you have carried out validation) rejects inputs that are not sensible.
2.	Test that the outputs the database produces are correct. These outputs might be on forms or reports or be the results of running queries.
3.	If you have created any macros you will need to test that these perform the correct actions at the correct times.

The Test Plan

You should created a test plan that lists all of the tests you will carry out on your database. In the test plan you should state :

• What the purpose of the test is.
• What test data the test will use.
• The type of test data that will be used (you should use all three types of test data).
• What results you expect to get when the test is carried out.

If your database is being produced as a piece of coursework it is a good idea to give each test a number.This will allow you to link the tests in your plan to evidence you later produce to show that you have carried them out.

Test Results

When you carry out the tests of your database you need to check that the actual results you obtain match the results you expected to get. If they do not then you will need to work out why not and try to correct the problem. You will then need to carry out the test again.

If your database is being produced as a piece of coursework you should collect evidence to show that you have carried out the tests and cross-reference this evidence to the descriptions of the tests in the test plan.

12.19. Databases : Summary

1.	A database is a computerised record-keeping system.
2.	Databases let you search through large quantities of data very quickly to answer questions.
3.	Data stored in a database must have a standard, regular structure.
4.	It is likely that you will encounter two different types of database package : Flat File A flat file database package will only let you store one file/table in each database you create. Relational A relational database will let you create many files/tables to represent different types of objects within each database you create. Links or relationships can be established between the different files in a database. Relational databases are considerably more sophisticated than flat file databases.
5.	A field is a single item of data stored in a database such as age or car registration number. Each field is identified by a field name.
6.	A record is a collection of fields that store all of the information about a person or thing.
7.	A file (or table) is a collection of records, each of which has the same structure.
8.	The structure of a record refers to : The names of the fields in the record. The data types of the fields in the record. The lengths of the fields in the record.
9.	The data type of a field determines what information can be stored in the field. Example data types are alphabetic, date and boolean.
10.	Fields can be either fixed or variable length.
11.	Data that is stored in a database is often coded to reduce the amount of storage space it requires and speed up data entry.
12.	Usually one particular field of each record contains an item which is used to identify the record. This field is called the key field. The value in the key field must uniquely identify each record.
13.	Forms can be used to create a user interface that makes it easier for a database user to enter and access data.
14.	Many databases will validate data as it is entered to check that the data is sensible, but not that it is correct. Validation checks such as presence checks, type checks, length checks and format checks can be used.
15.	A query is used to search the data in a database to locate records that match conditions entered by the user.
16.	A report is used to display data stored in a database. A report will let you decide which fields to display, where to display them, what statistics to calculate from the data and how to sort and group records. Reports can be either tabular or columnar.
17.	The records in a database can be sorted into any order to make the information that is stored easier to use.
18.	A macro is a short sequence of instructions that will automate a task. People who make databases often create macros to simplify the use of a database. Macros are often executed when users click on buttons on forms.
19.	Data can be imported into and exported from a database using a standard file format such as CSV or TSV.
20.	Relational databases have two important advantages over flat file databases. They are : Control Over Redundant Data : Wherever possible data is only stored once, so storage space is not wasted Data Consistency : Because each data item is stored only once it is not possible for the same item to store two different values, hence the data will always be consistent.
21.	It is important that you design and test properly any database that you create.

13.1. Spreadsheets : Introduction

A spreadsheet package is used for performing calculations and drawing charts. When you open a spreadsheet package the screen displays a very large table similar to this :

The table is divided into a number of boxes called cells. You can type information into each cell. Going across the table are many rows each of which is identified by a number. Going down the table are many columns each of which is identified by a letter.

Each cell is identified by a unique name called a cell reference. The cell reference is formed by writing down the letter of the column that the cell is in followed by the number of the row that it is in.

Groups of joined cells are known as a range. A range can be described by writing down the cell references of the cells at the top left and bottom right corners of the range with a colon to separate them.

You can enter three different types of information into a cell. The three types are :

• Numbers : Any number.
• Labels : Combinations of letters and numbers used as titles or labels to make the sheet clearer.
• Formulas : Used to carry out calculations with the numbers that are entered into the sheet.

Whenever any numbers are changed the calculations worked out by the formulas will be recalculated.

13.2. Spreadsheets : Exam Marks Example

This simple spreadsheet is used to calculate exam marks. The marks of each pupil in the two separate papers which make up the exam must be typed in. Formulas are then used to calculate each pupil’s total mark and the average mark for the whole class in each paper.

The first diagram shows the numbers, labels and formulas that were typed in. The second shows the answers that were calculated by the spreadsheet.

13.3. Spreadsheets : Formulae

A formula carries out a calculation using numbers that have been typed into the spreadsheet. The answer appears in the cell you type the formula into. In most spreadsheets formulas always start with a special symbol such as the equals sign. Some simple example formulae are :

When you change any numbers the results of the formulas that use the numbers will be recalculated.

13.4. Spreadsheets : Functions

Formulae can sometimes become very long if you want to include a lot of numbers in the calculation. Long formulae are tedious to type and can lead to errors. Consider a formula to add up fifty numbers in column A :

= A1 + A2 + A3 + A4 + … + A50

Functions can be used in formulae to make some calculations simpler to carry out. Functions often act on ranges of numbers. Important functions supported by most spreadsheets include :

Most spreadsheets have many more functions than this. They will include financial, statistical and database functions.

13.5. Spreadsheets : Replication

Often you will want to use several similar formulae in a spreadsheet. In the spreadsheet below a formula which is nearly the same is used to calculate each student’s total mark. The formula is changed slightly for each pupil because their marks are on different rows.

To avoid the need to type a similar formula in the three formulas in rows 3 to 5 can be generated automatically using the formula in row 2. To do this you must :

• Type the first (base) formula =B2+C2 into cell D2.
• Select the cells from D2 down to D5.
• Choose the spreadsheet's fill down option if it has one or use copy and paste.

Copying a formula like this is known as replication. If you want to copy a formula along a row rather than down a column you can use the fill right option instead. Because the formula changes as you copy it is known as a relative formula, or relative reference.

Sometimes you may not want a reference to a cell to change when a cell is copied in this way. To prevent a cell reference in a formula changing when you copy it you should precede the letters and numbers in the reference by a $ sign. Look at this formula :

=D3* $A$1

If you chose the fill down option with this formula the next row will contain the formula =D4*$A$1, the one after the formula =D5*$A$1 and so on. The first cell reference D3 changes but the second, A1, does not. Because the A1 reference does not change it is known as an absolute reference.

• A Relative Reference changes when it is copied to another place in the spreadsheet.
• An Absolute Reference does not change when it is copied to another place in the spreadsheet.

As well as fill down and fill right, the usual cut, copy and paste operations can be used to copy (or replicate) formulas.

13.6. Spreadsheets : Series

You may wish to put a series of numbers or values that follow on from each other into a row or column on your spreadsheet. Most spreadsheets have a fill series operation to do this. Example series include :

• 1, 2, 3, 4, 5, 6, 7
• 8, 10, 12, 14, 16, 18
• January, February, March, April, May
• 1/1/97, 2/1/97, 3/1/97, 4/1/97

To put a series of values into a cell you will need to :

• Type the initial (first) value into the cell you want it to appear in.

• Select the cells you want the series to be put into, including the first value.

• Choose the fill series option.

• You may then have to enter the step that the series should increase by each time.

13.7. Spreadsheets : Condition Functions

The spreadsheet can use a condition function to make a decision based on a value stored in the spreadsheet. The formula :

= IF(A1>=100,"Boiling","Not Boiling")

will output the message "Boiling" if the contents of cell A1 is greater than or equal to 100 and will output the message "Not Boiling" otherwise.

If statements can be nested (put inside each other) to give more than two responses based on several conditions. The formula :

= IF (A1<=0,"Frozen",IF(A1>=100,"Boiling","Liquid"))

will display "Frozen" if A1 contains a value less than or equal to 0. Otherwise, if A1 contains a value greater than or equal to 100 it will display "Boiling". If neither of these are true it will display "Liquid".

13.8. Spreadsheets : Database Functions

Most spreadsheets include database functions which can be used to treat a table in the spreadsheet as if it were a database. These functions typically let you search through the table to lookup information. A common spreadsheet has a VLOOKUP function which looks down a table to find a value. It is most easily understood by using an example.

This section of a spreadsheet is a table containing information about cars.

The column titles are the field names. Each row (apart from the top one) contains a record.

The formula =VLOOKUP("Corsa",A2:C4,2) will look down column A cells A2 to A4 for the value "Corsa". If it finds it, it will return the value in the same row but two columns to the rights, which is the price of a Corsa, £8,295. If the value "Corsa" was not in the list then the formula would display an error message.

The HLOOKUP function is similar to VLOOKUP except it looks along rows for data instead of looking down columns.

13.9. Spreadsheets : Sorting

A spreadsheet's sort function will let you put the data in a table into order using any of the columns of data in the table. To sort data in a spreadsheet you will need to :

• Select the area of the spreadsheet that contains the data to be sorted.
• Choose which piece of information in the table you want to use to order the data.
• Select whether you want to put the data in ascending (going up) or descending (going down) order.

The data in this table has been sorted :

To perform the sort the table range (A2:C4) was selected. The table was then sorted using the data in column A into ascending order. Note that row 1 was not included in the sort range because it contains the titles for the table rather than data.

13.10. Spreadsheets : Formatting

Information in spreadsheet cells can be formatted like text in a word processor. The font can be changed and information can be aligned to the left, right or centre of a cell. Titles can also be centered across multiple columns. Borders can be placed around cells to make distinct tables and cells can be filled with colour to make a spreadsheet clearer. Changing the appearance of the information in a cell like this is known as changing the cell format.

The appearance of numbers in cells (called the data format) can also be controlled. Example formats you may want to apply to a value in a cell are :

• Set the number of decimal places the value is displayed to.
• Display the value as a currency. E.g. display 2300.5 as £2300.50.
• Display the value as a percentage. E.g. display 0.876 as 88%.
• Display the value as a date.

You should also be able to change the width of columns and the height of rows to suit the data that has been typed in. If necessary extra rows or columns can be inserted into the spreadsheet and unwanted rows or columns can be deleted.

13.11. Spreadsheets : Charts

Charts can be created from data in a table in a spreadsheet. To create a chart you will need to :

• Enter or calculate the figures for the chart and put them into a table.
• Select the table.
• Choose the chart drawing option.

To draw a chart you will need to set a number of options such as :

• What type of chart (e.g. line, bar, pie) do you want ?
• How should the chart and axis be labelled ?
• Do you want gridlines or a border on the chart ?
• Do you want a legend to label different bars or lines on the chart ?

When you save a spreadsheet the charts you have drawn from it will be saved with it. If you change any of the figures on your sheet the charts should change automatically.

Alternatively, a specialised charting package could be used to produce a chart.

13.12. Spreadsheets : Macros

A macro is a short sequence of instructions that will automate a task. Using macros can save you a lot of work when you are using a spreadsheet by carrying out repetitive tasks for you. Not all spreadsheet programs will let you use macros.

Consider a spreadsheet which shows the league positions of some football teams in a league. Whenever a team plays a match the team's points score and position in the league may change. You will need to sort the data in the spreadsheet to put the teams into points order after each match. To sort data in most spreadsheets you will need to follow these three steps :

• Select the area of the spreadsheet that contains the data to be sorted (the league table).
• Choose which piece of information (e.g. points) in the table you want to use to order the data.
• Select whether you want to put the data in ascending or descending order.

Manually completing this process every time a team played a match would be very time consuming. Instead a macro can be created that will automatically carry out the three steps for you. Once a macro is created you can carry out the entire process by simply executing (or running) the macro.

Creating A Macro

A macro can be created by either programming or recording it.

When a macro is being designed a flowchart is often used to show the sequence of actions that the macro should carry out.

Executing A Macro

Every macro must have a name to identify it. When a macro is selected and its macro instructions are carried out the macro is said to be executing or running. There are two ways that you can execute a macro :

• From A Menu : If you choose the macro's name from the spreadsheet's macro menu it will automatically be executed.
• From A Button : Macros can usually be assigned (linked) to buttons which you can create on the spreadsheet. If you press a button it will run the macro that has been associated with it.

13.13. Spreadsheets : Validation

Sophisticated spreadsheet packages can validate data that a user enters into a spreadsheet to ensure that it is sensible. Data is validated as it is typed into a cell. Validation checks are specified at the time that the spreadsheet file is created. Here are some common types of validation checks that can be carried out by spreadsheet software :

Validation Checks
Presence Check	Checks that data has been entered into a cell and that it has not been left blank.
Type Check	Checks that an entered value is of a particular type. e.g. check that age is numeric.
Length Check	Checks than an entered value e.g. surname is no longer than a set number of characters.
Range Check	Checks that an entered value falls within a particular range. For example the age of a person should be in the range 0 to 130 years.
Format Check	Checks that an entered value has a particular format. e.g. a new-style car registration number should consist of a letter followed by 1 to 3 numbers followed by 3 letters.
Table Lookup Check	Checks that an entered value is one of a pre-defined list of valid entries which should be allowed.

13.14. Spreadsheets : Applications

Spreadsheets are used for applications (jobs) which involve calculation or graph-plotting. Some example application areas are :

13.15. Spreadsheets : What-If Problems

Spreadsheet models (a type of simulation) can be used to investigate what happens when variables in a model are changed. For example here is a simple model of the cost of producing a packed lunch :

The model uses formulas to calculate the total cost of producing a packed lunch from the individual costs of the items and the quantities required. It could be used to answer questions such as :

Because the values in column E are calculated using formulas when the values typed into the spreadsheet are changed the totals are automatically recalculated. It is for this reason that spreadsheets are often used to answer "what-would-happen-if" (or "what-if") problems. Once the formulas have been created, the effects of changing values can be determined easily and quickly.

Spreadsheets can be used to answer much more complicated questions. Typical "what-if" problems could be :

13.16. Spreadsheets : Why Use a Spreadsheet ?

There are many reasons why you might want to use a spreadsheet to perform some calculations rather than carry them out by hand. Some good reasons to use a spreadsheet include :

13.17. Spreadsheets : Designing A Spreadsheet

You should follow these eight steps to help you design a spreadsheet :

13.18. Spreadsheets : Testing

What To Test

After you have created a spreadsheet you need to test it to ensure that it is working properly. There are three main areas that you need to test. They are :

1.	The most important thing to test is that the formulae in the spreadsheet produce the correct answers.
2.	If you have carried out any validation you need to check that valid inputs are accepted and invalid inputs are rejected.
3.	If you have created any macros you will need to test that these perform the correct actions at the correct times.

There are two different methods that you can use to test your formulae. They are :

• By hand (or calculator!) calculate the results that you expect to get from your spreadsheet if it works. Then compare these to the results that your spreadsheet actually produces. Do they agree or not ? You can help yourself out by putting figures into your spreadsheet that will make the calculations easy to carry out manually.
• Try changing some figures in your spreadsheet. When you do this check that other figures change as you would expect them to. For example if you increase the number of chocolate bars sold in a week do the profits for that week increase correctly ?

The Test Plan

You should created a test plan that lists all of the tests you will carry out on your spreadsheet. In the test plan you should state :

• What the purpose of the test is.
• What test data the test will use.
• The type of test data that will be used (you should use all three types of test data).
• What results you expect to get when the test is carried out.

If your spreadsheet is being produced as a piece of coursework it is a good idea to give each test a number.This will allow you to link the tests in your plan to evidence you later produce to show that you have carried them out.

Test Results

When you carry out the tests of your spreadsheet you need to check that the actual results you obtain match the results you expected to get. If they do not then you will need to work out why not and try to correct the problem. You will then need to carry out the test again.

If your spreadsheet is being produced as a piece of coursework you should collect evidence to show that you have carried out the tests and cross-reference this evidence to the descriptions of the tests in the test plan.

13.19. Spreadsheets : Summary

14.1. Charting : Introduction

Numerical information can often be presented more simply as a chart (or graph) than as a table of numbers. Patterns in a series of numbers can be identified more easily when the numbers are represented visually. Charts can be produced using a specific charting package or by a spreadsheet.

A computer package can automatically draw a chart from a table of numbers that you have entered or calculated. You will need to decide on what type of chart you want and how the axis should be set up and labelled. If you change any of the numbers in the table then the computer will update the chart. A finished chart could be printed or included in a desktop published document.

14.2. Charting : Types of Chart

There are many different types of chart such as pie charts, bar charts, line charts and scatter graphs. The most appropriate type of chart to use will depend upon what the data is that you are using and what you are trying to find out or show.

Pie Chart
Purpose
Used to show how a quantity is divided up between a number of options.
Example Use
Show what proportion of people travel to school by each of five different methods e.g. bus, car, walk, bike, other.

Line Chart
Purpose
Used to show how a continuous quantity changes over time.
Example Use
Chart of how the temperature changes throughout the year.

Bar Chart
Purpose
Used to show how frequently a particular option is selected from a list.
Example Use
Chart showing how many people choose to shop at each of three different locations.

Scatter Graph
Purpose
Used to investigate relationships between two sets of data. A best fit line or curve is often drawn to show a relationship if one exists. The package may be able to produce this line for you.
Example Use
Investigate if taller people have bigger feet.

Most charting packages will produce other types of chart such as stacked bar charts or 3 dimensional pie charts. When choosing the best type of chart to use the most important point to consider is that the information can be clearly understood.

14.3. Charting : Axis, Labels and Legends

Labels

Once a chart has been created it is important that appropriate labels are added to it so that it is clear what the chart shows. All charts need a title to state what the purpose of the chart is.

If a chart has axis then each axis should have also a label. The axis running along the bottom of the chart is the X axis and the axis running up the side of the chart is the Y axis. An axis label should clearly state what the axis measures and what units have been used on the scale.

Axis Scales

When you draw a chart by hand you need to decide what range the axis will cover, i.e. what will be the lowest value you will plot on the axis and what will be the highest value. You also need to decide how you will divide the axis up, i.e. into steps of 5, 10, 50 etc. This axis has a range of 100 to 200 and goes up in steps of 50 :

If you use a charting package to produce a chart then it will automatically set the axis ranges and steps for you by looking at the data you have entered. However in some circumstances you may want to adjust these manually. Most charting packages will let you do this. You need to be careful that when you adjust the axis ranges you do not move any data points off the chart.

Legends

Sometimes you may want to show more than one set of data on the same chart. For example :

• You may want to show the temperature in each month of two different years to show that one year had a warmer summer than the other.
• You may want to show how the time it takes for a liquid to cool is different when the liquid is placed in two different shaped containers.

If this is the case then both sets of data are plotted on the same chart using different colours or patterns to distinguish them. A legend or key is then added to identify the two sets of data.

14.4. Charting : Summary

1.	Numerical information can usually be more easily understood if it is presented as a chart (or graph).
2.	Charts can be created in a specialised charting package or a spreadsheet.
3.	The most popular types of chart are :

Type	Use
Pie Chart	Shows how a quantity is divided up between a number of options.
Line Chart	Shows how a continuous quantity changes over time.
Bar Chart	Shows how frequently a particular option is selected from a list.
Scatter Graph	Used to investigate relationships between two sets of data.

15.1. Web Design : Introduction

The World Wide Web (or simply Web) is the most popular service on the Internet. The development of the web was partly responsible for the rapid increase in the number of people who used the Internet in the late 1990s. The World Wide Web consists of millions of different sites, each of which contains information. Each site is identified by a unique address called a Uniform Resource Locator or URL.

The information at a site is stored in the form of pages which can contain text, pictures, sound and video. Because web pages can contain so many different types of information they can be designed to be attractive, informative and interesting.

The different pages at a site can be linked together so that the user can move easily between them. A hyperlink is placed on a page to create a link to another page. Clicking on a hyperlink will move you to the page that the link joins to. Links can be made between pages at the same site and pages at different sites.

To view the information at a web site you must use a browser package. Web pages are stored in a special code called Hypertext Markup Language or HTML. To create a page you must either :

For must users the best option is to use a web design package. This will do most of the technical work for you. You simply design your page on the screen and the web design package creates the HTML code for the page you have made.

Whilst you are developing a web site you will probably store it on the hard disk of your computer. When it is complete you will need to upload it onto a web server so that other people can access it.

15.2. Web Design : Site Structure

A web site is usually made up of many pages. The first steps in designing a web site are to decide :

You will then need to decide how the pages will be linked together. You can use hyperlinks so that a person viewing the web site can move between the individual pages. You can also link your web site to other sites.

One way to show how your web site will be organised is to draw a diagram showing what will be on each page and how the pages will be linked. The diagram below shows how a web site for a football club could be organised.

The main page that the user starts at is the home page. The web site has been divided into five different sections which are club history, player statistics, team news, chat area and fixtures. In each section there are a number of pages. The arrows indicate links between the pages. The club will also make links to the web sites of other clubs that it will be playing. It hopes that in return these other clubs will create links to its web site.

Once the structure of the web site has been decided, you can start to create the individual pages. If there are a lot of pages to make then different people could work on each one. It is a good idea to make all of the pages on a site look similar. You can do this by using a standard page layout for each page.

15.3. Web Design : Page Layout

Most web sites are made up of many pages. It is a good idea to make all of the pages at a site look similar. This means that a person viewing the pages can tell that they are part of the same site.

You can make a page look consistent by using the same colours and styles for the text and the same background on each page. This diagram shows an example layout for a web page :

The designer of the web page has made these decisions about its layout :

• The background colour will be pale blue.
• Headings will be green and in the middle of the line.
• Normal text will be black.
• Pictures will be displayed with a thick black border around them.
• Options available to the user will be displayed at the bottom of the page.
• All options will be displayed as pink icons with labels on.

The basic layout of each web page on the site will be the same as this. Some pages will have more or less pictures. Some may have more options and some will have several headings, but they will all conform to the design points listed above.

Every time you create a web page you can specify what the background will be like, what the title will be and what normal text and hyperlinks will look like.

Background

You can choose a background colour for a page or you can put an image in the background. If you choose to use an image in the background then it should be a small one. If the background image is too large it will take a long time to load the page. Many web users will not be prepared to wait. The image should also be simple so that it does not interfere with the text that appears in front of it.

The background image is repeated up and down the page to fill up the whole screen. This is called tiling.

Page Title

A web page needs a title. This does not appear on the page itself. Instead it is displayed in the title bar of the web browser when the page is viewed.

Default Colours

You can set the default colours that should be used on a page. As well as the colour of the background you can also specify :

• The default colour for normal text.
• The default colour for a visited hyperlink.
• The default colour for an unvisited hyperlink.

15.4. Web Design : Text Style

When you produce a word processed document you can choose what fonts and sizes to use from a list of fonts that are installed on your computer. You can get your document to look exactly how you want it to.

Designing a web page is more difficult. This is because different computers have different fonts installed. If you use a particular font on a page you can not be sure that a person reading the page will have the same font. Web design packages use two different approaches to overcome this problem.

Styles	A range of pre-defined styles which each have a name can be selected. As well as normal text there are six types of heading and several other styles. When you design a web page you use these styles. You do not know exactly how the text will appear when it is looked at but you know that heading style one will stand out more than heading style two and so on.
Font Matching	Using font matching you can pick the font and font size that you want to use for your text from the fonts that are installed on your computer. If a person who looks at your web page does not have the same font his web browser will use the most similar font that is available. To increase the probability that another person has the same font as you it is a good idea to only use common fonts such as Times New Roman or Arial. Font matching only works with newer web browsers.

Font Style

Each font can have a range of extra styles applied to it. The three common styles that can be used on a web page are :

• Normal : No special style is applied to the font.
• Italic : The font will be displayed as if it is leaning slightly to the right.
• Bold : The lines used to draw the font will be drawn extra thick to make the text stand out.

Underline style can also be used on web pages but this is not normally done. This is because hyperlinks are underlined so underlined text could easily be mistaken for a hyperlink.

Alignment

Alignment describes the position at which text appears on a line on the page. On a web page, text can be aligned to the left, center or right of the page.

Font Colour

The colour of text can be specified. Most web pages make use of lots of colour because they are displayed on monitors which can easily show colour. If it is likely that your page will be printed out then you should check how the colours you have chosen look on a black and white printout as some colours do not show up very well.

15.5. Web Design : Graphics

Web design packages do not usually include a facility to let you create images. Instead you must obtain an image from another piece of software and bring this into the web design package. This is known as importing. The three most likely sources of images are :

• Images can be created from scratch in a graphics package.
• Images can selected from a clipart library.
• Photographs can be taken with a digital camera or scanned using a scanner.

Images take up a lot more storage space than text does. When a person looks at a web page the files that make up the page must be transferred over the Internet to his computer. If a web page contains an image it will take a lot longer to access than a text only page.

To speed up page loading, images on a web page must be stored in one of two special formats. These formats are GIF and JPEG. Both formats compress the image data so that it can be loaded more quickly.

Images in other formats such as bitmaps must be converted to one of these formats before they are put on a web page. A web design package will probably do this automatically.

15.6. Web Design : Hyperlinks

A hyperlink is a connection between two web pages. If you select a hyperlink on a page then you will be taken to the page that the hyperlink joins to. Hyperlinks can be represented as either text or a small image known as an icon.

A Text Hyperlink	An Icon Hyperlink

This diagram shows three web pages which are part of a site about the North West of England.

Clicking on the Manchester hyperlink on the main North West page would take you to the page about Manchester. Clicking on the cotton hyperlink would tke you to the page about cotton.

Most web browsers display links that you have visited in a different colour to links that you have not visited. Unvisited links are normally blue.

To create a hyperlink on a web page you normally type the text that you want the user to click on or import the image for the icon. Then you select the text or icon and identify which page the link goes to.

Sometimes when you click on a hyperlink it does not work because the page that it should link to does not exist. Most web design packages will automatically test the web site that you create to make sure that all of the links work.

15.7. Web Design : Hot Spots

A hot spot is an area of an image which acts as a hyperlink. When a person clicks on a hot spot a hyperlink is followed to another page. The person viewing the web page can not see where the hot spots are but when the mouse pointer moves over a hot spot it will change shape.

This image of a computer could be used on a web site about computers. It contains five hot spots but they are invisible.

This is the same image but with the hot spots highlighted in colour. They would not normally be visible.

If the user clicked on the image over the light blue hot spot he would be taken to a page about monitors. Clicking over the yellow hot spot would take the user to a page about keyboards.

Hot spots are either rectangular or elliptical in shape. To create a hot spot on an image you simply need to select the area that the hot spot should cover and then specify what page should be loaded when the mouse is clicked in this area. You can create any number of hot spots on an image but they should not overlap with each other.

15.8. Web Design : Tables

Tables can be used to set data out neatly like this :

When you create a table you specify :

• How many rows and columns the table should have.
• How wide each column should be.
• What colour the cells in the table should be.
• What style of border should be drawn around each cell (or if no border is required).

The height of each cell will automatically adjust so that the information that you type into it will fit. It is also possible to merge adjacent cells in a table together to form merged cells which cover more than one row or column.

Using Tables For Page Layout

Tables can also be used for a second purpose. When you create a web page you can not simply position text and pictures wherever you want on the page as you could with a desktop publisher. If you want to create complicated page layouts with multiple columns of text then you can use tables to achieve this effect.

Suppose that you wanted to create a page like this :

This can be achieved by creating a table and merging the cells in the table together to form the shapes required for the different sections of the page.

The information that is to appear on the page can be typed into the cells of the table. You can place any type of information, including pictures and other tables in a cell.

15.9. Web Design : Frames

Frames are used to create web pages where one section of the page can be changed independently of another section.

This is often done when web sites have a navigation panel at the side or bottom of the page. The panel contains icons which can be used to switch between the pages on the site. Selecting one of the icons will change the page that is displayed on the main part of the screen, but the navigation panel will remain the same.

Each frame is identified by a name. When a hyperlink is created the web designer can specify which of the frames to load the link page into when it is selected.

15.10. Web Design : Forms

A form is used to obtain feedback from the people who use a website. Forms can be used to gather people's opinions about a site or to gather information that a company or organisation might want.

Forms can be built up from several different types of controls. Some of the most important ones are shown in this table.

Short Text Entry	A short text entry box lets the user type in information. The web designer can specify the maximum number of characters that can be typed.	What is your surname ?
Long Text Entry	A long text entry box lets the user type in information. The text input area can be scrolled to allow a lot of text to be entered.	Please enter your comments on this site :
Radio Button	Radio buttons let the user select one or more options from a list. The web designer chooses how many options can be picked at once.	Are you male or female ? Male Female
List Box	A list box lets the user choose one option from a list.	Please select your age group : Select Age Under 16 16-20 21-30 31-60 Over 60
Push Buttons	Buttons are used to start actions such as sending the contents of the form or clearing the form.

When a form has been completed the data that the user has entered must be sent to the person who runs the website. This can be done by transmission by email or by saving the form contents to a file on a web server.

15.11. Web Design : Advanced Design Tools

There are many different technologies which can be used to enhanced a web page. Some of these will only work with newer web browsers. Others require an extra piece of software called a plug-in to be installed in addition to the browser. Some of these additional technologies are listed below.

15.12. Web Design : Uploading

Whilst you are developing a web site you will probably store it on the hard disk of your computer. When it is complete you will need to upload it onto a web server so that other people can access it.

A web server is a computer which stores web pages. It responds to requests to view pages from other computers by sending the required pages to them. Many web servers are connected to the Internet.

Some web servers are not connected to the Internet but are connected to a private network that is owned by a company. If this is the case then only people within the company will be able to view the pages on the server. This is known as an Intranet.

The process of transferring your web site onto a web server is known as uploading. A service called File Transfer Protocol (FTP) is used for this purpose.

15.13. Web Design : Summary

1.	The World Wide Web (or simply Web) is the most popular service on the Internet.
2.	Each site on the World Wide Web is identified by a unique address called a Uniform Resource Locator or URL.
3.	A web site is made up of pages. Pages are joined together by hyperlinks.
4.	To view a web site you need to use a web browser package.
5.	Web pages are stored in a language called HTML. To produce a web page you can either write the HTML code yourself or use a web design package.
6.	The structure of a web site refers to the organisation of the pages at the site and which pages are linked to which other pages.
7.	Usually all of the pages that are part of a web site have the same page layout. They will share a common background, colour scheme, text styles etc.
8.	It is possible to choose the fonts that you want to use on a web page, but these may not be present on every computer. Often special text styles are used instead.
9.	Images can be included in web pages. These need to be fairly small so that they do not take too long to download. Images on web pages are usually stored in compressed GIF or JPEG format.
10.	Hotspots can be created on images. A hotspot is an area of an image which acts as a hyperlink.
11.	Tables can be included in web pages. They are often used to create complicated page layouts such as multi-column pages.
12.	A page can be divided up into frames so that the contents of one section of the page can be changed independently of the other section(s).
13.	A form can be included on a web site. The form can be filled in by a person visiting the site and the information entered on it can be sent back to the page's owner.
14.	Advanced tools such as Javascript, Java and Video can be used to enhance the appearance of a web page.
15.	Whilst you are developing a web site you will probably store it on the hard disk of your computer. When it is complete you will need to upload it onto a web server so that other people can access it. File Transfer Protocol (FTP) is usually used for this purpose.

16.1. Multimedia : Introduction

The term multimedia literally means using more than one medium. In the context of computer software the term multimedia means that information is conveyed using more than one method. Methods widely used to convey information include :

• Text
• Drawings
• Photographs
• Sound
• Music
• Videos
• Animations

The use of advanced methods of information display such as video and music can significantly enhance the quality of computer packages and presentations.

16.2. Multimedia : Hardware Requirements

Text and drawings can be displayed by practically any computer. To play sound and music a computer may need to have a sound card fitted. To play video a computer will need a fast microprocessor and quite a lot of RAM.

Text and drawings take up very little storage space. Sound takes up more storage space and video needs a lot of storage space. Because multimedia information requires a lot of storage space packages which use multimedia are usually supplied on CD-ROM or DVD. If you create your own multimedia work then you will need a lot of free space on your hard disk.

16.3. Multimedia : Applications

Here are some common uses of multimedia presentations.

Reference CD-ROMs

Reference works such as encyclopaedias are now available on CD-ROM. Tens of thousands of pages of written information can be put onto a single CD-ROM disk. Videos and animations can be used to explain important concepts and show important events. Sound can be used to play famous pieces of music and important speeches. Most reference CD-ROMS include a search facility where you can type in a description of what you want to find out about and the computer will search the encyclopaedia for you. A CD-ROM encyclopaedia is usually much cheaper to purchase than an equivalent encyclopaedia provided as a set of books.

The Internet

Information displayed on the World Wide Web is usually presented as a mixture of text and pictures. Sometimes sound is also used. Video can be incorporated into World Wide Web pages but this is not done very often. As video files are very large it is usually too expensive to transmit them over the Internet because it would take a long time.

Presentations

A multimedia authoring package lets the user put together many different types of information to make a single presentation. Multimedia authoring packages are rather like desktop publishers but they let the user include extra types of information such as videos which could not be included in a desktop published page. It does not make sense to print out multimedia presentations like this (you can not see sound) so multimedia presentations are usually viewed either on a computer monitor or using a projector.

Here are some common uses of multimedia presentations :

Computer Games

Computer games have always made use of animation. Many games now include video sequences and advanced sound effects as well.

16.4. Multimedia : Summary

17.1. Operating Systems : Introduction

The operating system is a very special piece of software. All the other applications software such as databases and spreadsheets communicate with the computer hardware through the operating system. The operating system controls the overall operation of the computer. It is the most important part of the systems software.

An operating system (or OS) is a computer program which controls the entire operation of the computer. Computer software applications communicate with the computer hardware via the operating system.

Example Operating Systems

When you buy a computer it is usually supplied with an operating system already installed. You will not be able to use a computer without an operating system. Different operating systems are available for different types of computer and different purposes. Some popular operating systems are :

The choice of operating system will affect how a computer works. It will probably determine the type of user interface (command line, menu driven or graphical) that the computer uses and the types of processing (batch, transaction or real-time) that the computer can carry out.

Because an application such as a spreadsheet works by communicating with the operating system the application will probably only work with one particular operating system. If you buy Microsoft® Works® for Windows® 2000 it will only operate on computers with the Windows 2000 operating system. If you want to use Microsoft Works with the MS-DOS® operating system you will have to buy a different version of the application.

MS-DOS®, Windows® 2000 and Microsoft® Works® are registered trademarks of Microsoft Corporation in the United States and other countries.

17.2. Operating Systems : Tasks

There are several tasks which are performed by practically all operating systems, regardless of the complexity of the computer the operating system is being used on. These tasks include :

• Managing communications between computer and connected peripherals.
• Providing a user interface.
• Allocation of computer memory.
• Organising data on backing storage devices.

The range of tasks that an operating system performs increases if the computer using the operating system is on a network or if the operating system is a multi-tasking or multi-user operating system.

Managing Communications Between Computer and Connected Peripherals

Many peripherals can be connected to a computer. It is the job of the operating system to manage the communication between the application programs that are running on the computer and the peripheral devices. For example the operating system will :

• Send and receive data to backing storage devices for the loading and saving of data and programs.
• Receive input data from peripherals such as a mouse.
• Send data for display to peripherals such as a printer or VDU.

There has to be some control over these activities to make sure that problems do not occur. Consider what might happen if a computer program was trying to load a file from a floppy disk and, at the same time, another program was trying to save data. Therefore the operating system manages all of these tasks. If, for example, a program wants to save or print a file it must send a request to the operating system asking it to do so. The operating system will then carry out the task.

Provision of a User Interface

The operating system will provide a user interface that the user uses to interact with the computer. Modern operating systems usually provide a graphical user interface. Alternatives to this are command line and menu driven interfaces.

Allocation of Computer Memory

Computer memory must be allocated to (divided between) the different tasks that the computer is performing. Even if your computer appears to be doing only one task such as word processing there will be several different items to which memory must be allocated. For example memory would have to be allocated to storing the word processor program, storing your word processed document and storing a copy of the image that is being displayed on the monitor. And of course the operating system itself will also use up some memory.

Organising Data on Backing Storage Devices

Work and programs must be saved on a backing storage device so that they can be kept when a computer is turned off. The operating system is responsible for organising data on backing storage devices. Work and programs are saved as files which must be organised so that they can be found and loaded when required. Each file is identified by a filename.

Most operating systems divide a backing storage device up into directories (also known as folders). Files can be stored within each directory. The diagram below shows how data has been organised on a particular hard disk drive.

• The main directory on the disk is known as the Root Directory. There are three directories in the root directory. They are Games, Programs and Work.
• Inside each of these directories there are other directories. For example in the Work directory there are three other directories called Geography, History and ICT. A directory inside another directory is known as a subdirectory.
• This type of organisation, where a directory can be created within another directory is known as hierarchical. The organisation of the directories is known as a directory tree.
• Dividing a disk up into directories makes it much easier to find files.

The user has chosen the names of the directories and files but the operating system has decided where and how to store the files on the disk. The operating system has ensured that no two files are stored in the same place on the disk and that rules such as having a maximum length for filenames have been enforced.

MS-DOS®, Windows® 2000 and Microsoft® Works® are registered trademarks of Microsoft Corporation in the United States and other countries.

17.3. Operating Systems : Advanced Operating Systems

The most basic type of operating system can only carry out one task at a time and can only be used by one person at a time. Sometimes a more sophisticated operating system is required. The three most common advanced operating systems are :

Operating System	Use
Network OS	Network operating systems are used on computers which are connected to a network to manage the security of the network.
Multi-Tasking OS	A multi-tasking operating system can appear to carry out more than one task at the same time.
Multi-User OS	A multi-user operating system is used on a mainframe or minicomputer which may be used by more than one person at a time.

These operating systems are more complicated and may require faster hardware and more memory to work than more basic operating systems.

17.4. Operating Systems : Network

Operating systems that are used on computers connected to networks usually have to carry out some additional tasks. Probably the most important of these is managing system security. Important aspects of systems security that an operating system might manage are :

• Making a user log on with a user name and password before a computer can be used.

• Allow a user on one computer to access files stored on another computer (e.g. a server).

• Controlling who has access to which files.

• Keeping a log of all of the files that a user changes.

• Automatically backing up important files.

17.5. Operating Systems : Multi-Tasking Operating Systems

A multi-tasking operating system is capable of appearing to carry out more than one task at a time.

Windows® 2000 and UNIX®; are examples of multi-tasking operating systems. If you have a computer with a multi-tasking OS you could be using a spreadsheet and a word processor at the same time. You could also have the computer testing every five minutes to see if you had any new email and displaying a television programme on screen. Most multi-tasking operating systems have a WIMP user interface with each task being displayed in its own window.

In reality because the computer only has one microprocessor it can only be doing one thing at once. The computer fools you into thinking it is doing more than one task at once by dividing the processor time up between each of the tasks. Each task is given a small amount of processor time in turn. The amount of time allocated to a task is known as a time slice. These time slices are very short, usually less that 1/1000 of a second. Because the slices are so small, the user is fooled into thinking that the computer is doing many things at once.

The time can be allocated to the different tasks on an equal basis (each tasks gets the same amount of time) or on a priority basis with more important or more urgent tasks getting most time. Commonly the task that the user is currently working on (such as entering data into a spreadsheet) has the highest priority. It is allowed exclusive use of the processor whenever it wants it and is known as the foreground job. Other less urgent tasks such as sending data to a printer are only permitted to use the processor when the foreground job does not need it. These tasks are known as background jobs.

If an operating system is carrying out more than one task then the job of allocating memory also becomes harder because the computer’s memory must be allocated between the tasks.

Multi-tasking operating systems are also sometimes known as multi-program operating systems.

Windows® 2000 is a registered trademark of Microsoft Corporation in the United States and other countries.

17.6. Operating Systems : Multi-User Operating Systems

Multi-user operating systems are used on large mainframe computers. A mainframe computer system has one very powerful processing unit which may contain many microprocessors. Many users will all share this processing unit. They use terminals (a keyboard and a monitor) to access the mainframe computer.

A multi-user operating system lets more that one user work on a mainframe computer at the same time.

A multi-user operating system allocates the CPU time of the mainframe computer between the different users. Each user in turn is given a small time slice of the CPU time. Because these time slices are very small the users believe that they are all using the mainframe at the same time.

This diagram shows how a mainframe computer with four terminals connected to it divides its processing time up.

Time can be shared equally between each user or can be allocated to users using a priority system so that some users get more time than others. Multi-user operating systems rely on having very powerful mainframe computers to process data.

17.7. Operating Systems : Processing

Sometimes operating systems are also classified according to the types of processing that can be carried out by software packages running on them. As well as the categories of network, multi-tasking and multi-user a particular operating system could fall into these four categories :

OS Type	Description
Batch	A batch operating system can perform batch processing of data. Data to be processed is grouped together into batches. No data is processed until a complete batch has been collected, then all of the data in a batch is processed in one go. There may be a long time delay between data being input into the system and the data being processed. Each task that is waiting to be carried out is known as a job.
Interactive	An interactive operating system carries out a dialogue with the user. Once the user has entered a command or selected an option the operating system will process the user's input and react with some output before the user can input any more data. Interactive operating systems can carry out transaction processing.
On-Line	An on-line operating system allows the user of a computer to interact directly with another central computer. On-line operating systems are commonly used by transaction processing systems that require many users at different computers to interact with a central computer. An on-line operating system could be used in a chain of travel agents where computers located at many branches make bookings on one central computer.
Real Time	A real time operating system can perform real time processing of data. This means it can process data extremely quickly to meet a real world deadline. Real time operating systems are usually used in control systems and embedded systems.

Note that a particular operating system could fall into more than one category. e.g. it could be network, multi-tasking, interactive and on-line.

17.8. Operating Systems : Summary

1.	The operating system (OS) is a computer program which controls the entire operation of the computer. It is the most important piece of systems software.
2.	MS-DOS®, Windows 2000® and UNIX are operating systems.
3.	The operating system will determine the type of user interface and types of processing a computer can use.
4.	All operating systems perform these tasks : Managing communications between computer and connected peripherals. Providing a user interface. Allocation of computer memory. Organising data on backing storage devices.
5.	Data saved on a backing storage device is usually organised hierarchially in a directory tree. Files are created within directories. Directories can also be created within other directories. A directory inside another directory is a subdirectory.
6.	There are three types of advanced operating system that can perform additional functions. These are : Type Use Network OS Network operating systems allow users to communicate with other computers on a network to perform tasks such as loading files and sending email. A network operating system must also control computer security. Measures such as username and password logons and logs will be used. Multi-Tasking OS Multi-tasking (or multi-programming) operating systems appear to be capable of carrying out more than one task at a time. Each task is allocated very small slices of processor time in turn. The different tasks can be allocated different priorities. The main task the user is interacting with is known as the foreground job and other less urgent tasks are known as background jobs. Tasks with higher priorities will be allocated more processor time. Multi-User OS Multi-user operating systems allow more than one user to work on a mainframe computer at the same time. Each user is allocated a small slice of processor time in turn.
7.	Operating systems are also sometimes classified according to the types of processing they can carry out. These additional classifications are : Classification Description Batch A batch operating system can perform batch processing of data. Interactive An interactive operating system carries out a dialogue with the user by the user entering commands and the computer responding. Interactive operating systems can carry out transaction processing. On-Line An on-line operating system allows the user of a computer to interact directly with another central computer. On-line operating systems are commonly used by transaction processing systems that require many users at different computers to interact with a central computer. Real Time A real time operating system can perform real time processing of data. This means it can process data extremely quickly to meet a real world deadline.
8.	A particular operating system might fall into several categories. For example it could be a multi-tasking, network, interactive OS.

MS-DOS® and Windows® 2000 are registered trademarks of Microsoft Corporation in the United States and other countries.

18.1. Other Software : Introduction

Most people use standard generic packages such as a word processor or database for much of their work. Many other generic or application specific packages are available to carry out particular tasks. Here are some examples :

Games	Games are programs which let people play in situations that they are unlikely to encounter in everyday life.
Teaching	Computer Aided Learning and Home/Distance Learning systems can help people to learn at their own pace.
Geographical Information Systems (GIS)	Geographical Information Systems plot stored data onto maps so that it can be easily analysed and interpreted.
Expert Systems	An expert system is an artificially intelligent computer system that stores and can apply knowledge about a particular area of human expertise.

18.2. Other Software : Games

The first computer games could only be played in an arcade on specially designed arcade machines, but now games can be played in several different ways :

• Games can be played on a home computer such as a desktop or laptop.
• Games can be played on a games console, a type of computer developed specifically for playing games.
• Games can be played on portable devices such as PDAs or cellular telephones.

Games usually include very high quality graphics and animation or video, together with excellent music and sound. Because these things require a lot of storage space most games are supplied on CD-ROM or DVD. To play the latest games on a desktop computer you usually need to have a lot of RAM and a fast processor. Most games are easier to play if you have an input device such as a joystick in addition to your mouse and keyboard.

In many games it is possible to play against the computer as an opponent. The computer may use a form of artificial intelligence to decide how to play. Newer games also let you compete against other people in different locations across the world via the Internet.

Some people believe that spending a lot of time playing computer games is a bad thing. They think that people who spend too long playing games don't do enough physical exercise to keep them healthy and may miss out on the opportunity to socialise with others. There are also concerns that peoples behaviour may be affected by the amount of violence contained in some games. An age rating system, designed to stop young children obtaining very violent games has been introduced.

18.3. Other Software : Teaching

Computer software can assist people to learn in many different ways. Two of the most significant are by using Computer Aided Learning (CAL) software and through Home/Distance Learning.

Computer Aided Learning (CAL)

A computer aided learning system teaches a user by presenting her with material to learn then assessing how well the material has been understood :

• First, information that the user must learn is presented. This could be done using text, graphics, videos etc. It may even be interactive with the user making choices about how they learn.
• The system then asks the user questions to determine how well she has understood the material.
• The system reviews what aspects of the material the student has and has not understood. The user will be provided with feedback about how well she has done.
• Future lessons may be tailored by the software to take account of the topics that the user finds easy or hard.

Home/Distance Learning

The widespread availability of computers in the home and fast broadband Internet links means that it is possible for people to study at home, with course material being delivered to them across the Internet.

• Learning material can be made available on the world wide web, to include text, graphics, videos etc.
• A learner can communicate with a tutor by email to submit work for assessment and to obtain help on difficult topics.

This type of learning is particular suitable for people who live in remote communities, who find it difficult to travel to a college or who move around frequently.

Advantages of using Computerised Learning Systems

There are several advantages to using a computerised learning system, including :

• The learner can progress at their own pace. The speed of progress is not dictated by the pace of a class.
• Learning can be done when it suits the learner, not the tutor. This is particularly useful to people who work and study in their spare time or who have to look after children.
• A computer can provide immediate, automatic feedback to a learner about how well they are doing.
• The knowledge of many qualified teachers or lecturers can be brought together in one system.

There is still however some way to go in developing these systems. Some current computer aided learning packages make fairly basic assessments of the student's knowledge. Additionally computer aided learning systems are inflexible and lack the prsonal touch of a teacher or lecturer.

18.4. Other Software : Geographical Information Systems (GIS)

A Geographical Information System (GIS) presents stored data graphically on a map. The most common use of a geographical information system is as part of an in-car satellite navigation (SatNav) system, used to give a driver directions to get to his destination.

Satellite Navigation (SatNav)

A satellite navigation system consists of a receiver, a computer, a CD-ROM or DVD-ROM drive, an LCD monitor and a keyboard or remote control.

The receiver receives signals from a network of satellites called Global Positioning Satellites (GPS). From these the computer system can work out the location of the car. Maps are stored on a CD or DVD and based on the position of the car the computer can load the correct map and display it on the monitor with the car's position indicated.

Before setting out on a journey the driver can enter the name or postcode of the place that he is travelling to. The computer can locate the destination on the map and work out the best route for the driver to take. As the journey progresses the monitor will be used to indicate when the driver should turn onto another road. Directions may also be announced through speakers using speech synthesis so that the driver does not have to take his eyes off the road.

A satellite navigation system may also be linked to a traffic information system which can receive information about traffic jams and roadworks by radio. If a road involved in a journey is busy the computer system will be able to automatically change the recommended route to minimise the delay.

Other Geographical Information Systems

Geographical information systems can also be used to help analyse data by plotting it on a map. For example :

• The Police could plot data about where crimes have been committed on a map to identify the areas that suffer from most crime so that they can deploy more officers in these areas.
• An insurance company could plot data about claims that homeowners have made on a map to help them identify what premiums to charge for house insurance in different areas.
• A political party could plot data about people who have promised to support it on a map to identify areas in which they should campaign to increase their support.

All of these tasks are made easier by seeing the data viewed on a map rather than as a list in a table. Most geographical information systems will be able to display a map at different levels of magnification so that as much or as litte detail as is required can be seen.

18.5. Other Software : Expert Systems

An expert system is an artificially intelligent computer system that stores and can apply knowledge about a particular area of human expertise. Expert systems store data collected from human experts in a knowledge base. An inference engine is used to apply this knowledge to solve problems posed by the user. Most expert systems ask the user questions and then suggest a conclusion to the user, based on the answers given to these questions. An expert system may be able to learn from experience, developing new knowledge or modifying existing knowledge based upon how accurate its conclusions have proved to be in the past.

The knowledge base is generally composed of rules that form conclusions based on the inputs made by the user. A simple example rule might be :

IF the person is aged 60 or over AND is female THEN she is entitled to a pension

An expert system will usually require many inputs and apply many rules before offering a possible conclusion to a user. The expert system may change the questions that it asks the user, based on the answers entered to previous questions. Here are some example uses that expert systems can be put to :

Expert systems are useful because

• An expert system can be used anywhere, at any time. A human expert is not always available.
• An expert system can contain the knowledge of many experts, not just one.
• Once it is set up an expert system can be used very cheaply. Experts usually demand high fees as their knowledge is valuable.

However an expert system is only as good as the knowledge it contains, and expert systems may not recognise unusual situations that a human expert would spot.

18.6. Other Software : Summary