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.

GCSE ICT Companion 04 - (C) P Meakin 2004