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5.3.1 Computer memory

Revision Points:
Candidates are expected to be able to:
  • identify the difference between RAM and ROM, describing their uses;

Typical memory chips arranged on a 'slot-in' boardRAM (Internal Memory)

Internal memory is usually referred to as RAM (Random Access Memory) because data can be stored and accessed from any area of the memory chip.  It is usually measured in mega-bytes (MB) so a typical desktop computer might be sold with 512MB of RAM.

All computers have main/internal memory to store programs and data while the computer is running. This memory is in the form of memory chips and the contents are lost when the computer is switched off (it is also know as 'volatile' memory).


ROM (Read Only Memory) is a type of memory chip which only allows data to be read from it. You cannot therefore change the data stored on ROM.  In a computer, ROM it is used often used to store the permanent programs and/or data needed to run the hardware. In an embedded computer, such as in a washing machine, the ROM stores the program that controls the machine. The contents of ROM are not lost (it is 'non-volatile') when a computer is turned off.


The motherboard BIOS (Basic Input/Output System) memory chip typically contains program code called firmware to access fundamental hardware components such as the keyboard, floppy drives, ATA (IDE) hard disk controllers, USB human interfaces, and storage devices. By providing access to the system hardware the BIOS enables the running of higher-level operating systems (DOS, Windows etc.) that are loaded from backing storage.

Early computer BIOS chips were ROM so the program could not be altered. As the need for updates grew, hardware manufacturers needed to issue BIOS updates to upgrade their products, improve compatibility and remove bugs. A modern motherboard BIOS therefore is made up of ROM and RAM, a small battery on the motherboard providing the power to maintain the contents of the RAM.

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