Storage : Immediate Access Store
Immediate Access Store ( IAS ) holds programs and data that the user is currently working with. For example :
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 operating system 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.
It is easy to add extra RAM to a microcomputer by inserting extra RAM cards called SIMM 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.
(C) P Meakin 2001