Systems architecture: RAM

The idea

RAM (Random Access Memory) is the main memory a computer uses while programs are running. It is volatile: its contents are lost when power is removed. The processor fetches instructions and data from RAM, and results are written back to it, so RAM must be directly accessible to the CPU. RAM holds the currently running programs, the operating system in use and the data being worked on. Because RAM is limited, a computer may need to manage which contents are held there. Read each option carefully: a distractor may describe ROM (non-volatile, holds start-up instructions) or secondary storage (long-term files). Choose the option that matches RAM's role as fast, volatile working memory.

What earns the marks

• RAM is volatile, so its contents are lost when the power is switched off.
• RAM holds the programs currently being executed, the data in use and the parts of the operating system in use.
• The CPU can read instructions and data from RAM and write results back to it.
• RAM is working memory used during processing, not long-term storage of files.
• RAM is distinct from ROM, which is non-volatile and holds start-up instructions.

Common mistakes and how to put them right

• Confusing RAM with long-term storage.

  Put it right: RAM is volatile working memory; files kept permanently belong in secondary storage.

• Describing RAM as non-volatile.

  Put it right: RAM loses its contents when power is removed, unlike ROM.

• Thinking RAM stores the start-up (bootstrap) instructions.

  Put it right: Those are held in ROM; RAM holds running programs and data.

Exam tips

• Underline the key word in the question (for example 'volatile' or 'currently running') before comparing options.
• Eliminate any option that describes ROM or secondary storage rather than working memory.
• Check that the chosen option is true of RAM in general, not just of one type of computer.