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AQA GCSE Computer Science

Memory and storage — AQA GCSE Computer Science revision

Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 7 minutes to read.

RAM, ROM and virtual memory

  • RAM (Random Access Memory) is volatile memory that temporarily stores currently running programs and data, and is lost when the power is switched off.
  • ROM (Read Only Memory) is non-volatile memory that permanently stores essential startup instructions, such as the BIOS, which cannot normally be changed.
  • Virtual memory uses space on secondary storage to act as extra RAM when physical RAM is full, allowing more programs to appear to run at once.
  • Using virtual memory is much slower than using RAM because secondary storage has a much slower access speed, so relying on it heavily can slow a system down significantly.

Cache and the memory hierarchy

  • The memory hierarchy arranges storage by speed and cost: registers are fastest and most expensive, followed by cache, then RAM, then secondary storage which is slowest but cheapest per gigabyte.
  • Cache exists in levels (L1, L2, L3); L1 is smallest and fastest, closest to the CPU core, while L3 is larger and slower but still much faster than RAM.
  • Storing frequently accessed instructions in cache reduces the time the CPU spends waiting for data from slower RAM.

Key terms

RAM
Volatile memory that temporarily stores running programs and data.
ROM
Non-volatile memory that permanently stores essential startup instructions.
Virtual memory
Space on secondary storage used as extra RAM when physical RAM is full.
Volatile
Describes memory that loses its contents when power is turned off.
Non-volatile
Describes memory or storage that keeps its contents without power.
Secondary storage
Storage that holds data permanently, such as hard drives or SSDs.

Common exam traps

  • Thinking RAM is permanent storage — it is volatile and loses data when power is lost.
  • Confusing ROM with RAM — ROM is read-only and stores startup instructions, not user programs.
  • Believing virtual memory is as fast as RAM — it is much slower since it uses secondary storage.

Practice questions with answers

  1. 1. Which type of memory is volatile?

    • • ROM
    • • RAM
    • • Hard disk
    • • Optical disc

    Answer: RAM

    RAM loses its contents when the power is switched off.

  2. 2. What is stored in ROM on most computers?

    • • User documents
    • • Startup instructions like the BIOS
    • • Currently running programs
    • • Downloaded files

    Answer: Startup instructions like the BIOS

    ROM holds essential permanent startup instructions.

  3. 3. What is virtual memory?

    Answer: Space on secondary storage used as extra RAM when physical RAM is full

    It lets the computer handle more programs than RAM alone could support.

  4. 4. Why is virtual memory slower than RAM?

    • • It uses less power
    • • It relies on slower secondary storage
    • • It is non-volatile
    • • It has more capacity

    Answer: It relies on slower secondary storage

    Secondary storage has much slower access speeds than RAM.

  5. 5. Which storage type uses spinning magnetic platters?

    • • SSD
    • • USB flash drive
    • • Hard disk drive
    • • DVD

    Answer: Hard disk drive

    HDDs store data magnetically on spinning platters.

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