Knowledge Organiser: RAM and ROM
Key Terms
- RAM: Random Access Memory — volatile, read/write, temporary storage
- ROM: Read Only Memory — non-volatile, stores permanent firmware
- Volatile: Loses all data when power is switched off
- Non-volatile: Retains data without power
- BIOS/UEFI: Firmware stored in ROM; runs when computer is first powered on
- Firmware: Permanent software instructions stored in ROM
Must-Know Facts
- RAM is volatile — loses all data when power is off
- ROM is non-volatile — keeps data without power
- RAM stores: running programs, open files, the operating system
- ROM stores: BIOS/UEFI boot instructions and firmware only
- RAM is read/write (fast in both directions); ROM is read-only
- More RAM = more programs can run simultaneously
- RAM is cleared on shutdown; ROM never changes (unless firmware update)
Key Concepts
- Why ROM stores BIOS: Must be available instantly on power-up, before OS loads, and must never be accidentally lost
- Why RAM must be volatile: Fast read/write speeds require different technology that needs constant power
- Memory hierarchy (fastest to slowest): CPU registers → Cache → RAM → SSD → HDD (ROM is not a speed-hierarchy tier — it stores the bootstrap/BIOS and is non-volatile, separate from the main hierarchy)
- Boot process: Power on → ROM provides BIOS → OS loads from storage into RAM → programs run in RAM
Common Mistakes
- Confusing RAM and ROM: RAM is volatile (loses data when power off) and holds running programs; ROM is non-volatile and holds permanent firmware — they are completely different
- Saying "more RAM makes programs run permanently": RAM only stores data while the computer is on — saving to secondary storage (HDD/SSD) makes data permanent
- Calling RAM "storage": RAM is primary memory (temporary working space), not storage — storage refers to HDDs, SSDs, and flash drives
- Saying ROM cannot ever be changed: Modern ROM (flash ROM) can be updated via firmware updates — but it cannot be written to during normal operation