Hardware and network technologies - CCEAInternal memory

Random Access Memory (RAM)

Otherwise known as main memory, this is the component of a computer that stores programs currently being executed, or data needed for immediate use. RAM is volatile, meaning its contents are lost if the computer loses power.

Overview:

• Volatile
• Used to hold programs and data currently in use
• Used to hold the operating system when the computer is switched on

Read Only Memory (ROM)

Some parts of a computer's memory are marked 'read only', which means their contents cannot be changed or deleted. The contents of ROM are safe when a computer loses power (non-volatile).

For these reasons, ROM is ideal for storing instructions that must not be lost or overwritten, such as the BIOS (Basic Input Output System) or the MAC address (in a network card).

Traditionally, the BIOS (the computer boot up instruction set) was always stored in ROM because it is non-volatile. However, flash memory (which is also non-volatile, but not read-only) is now often used for the BIOS so that changes to the instructions can be made.

A 'bootstrap program' loads the BIOS as well as any system data that does not change (for example, the hard disk and the amount of RAM installed).

Overview:

• Non-volatile
• Can be read from, but not written to
• ROM is used to hold basic computer hardware settings and, in the past, it held the BIOS to boot up the computer

Cache

RAM is comparatively slow to access when compared to the speed at which registers work. So, to help speed up the processing time, cache memory is used to store instructions or data that are either frequently used, have recently been used or are about to be used. This means they don't have to be fetched directly from RAM.

Overview:

• Instructions can be read, or written to
• Faster access speeds than RAM
• Small in capacity compared to RAM
• Stores frequently accessed program instructions
• The larger the cache capacity, the faster the CPU performance