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.

GCSE ICT Companion 04 - (C) P Meakin 2004