This key facts covers ROM - Read Only Memory within RAM and ROM for GCSE Computer Science. Revise RAM and ROM in 3.4 Computer Systems for GCSE Computer Science with 16 exam-style questions and 16 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 5 of 11 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
ROM - Read Only Memory
Definition:
ROM (Read Only Memory) is non-volatile memory that stores permanent instructions that rarely or never change. It retains its content even when the power is turned off.
Key Characteristics:
- Non-volatile: Keeps data permanently, even without power
- Read-only: Data is set during manufacturing or programming - cannot be easily changed by normal use
- Permanent storage: Contents remain unchanged for the device's lifetime (in traditional ROM)
- Slow write speed: If writable at all, writing is much slower than reading
- Critical instructions: Stores essential startup code that must never be lost
What ROM Stores:
- BIOS/UEFI Firmware: Basic Input/Output System - the first code that runs when you press the power button
- Boot instructions: Tells the computer how to start up and find the operating system
- POST (Power-On Self-Test): Checks that hardware components are working correctly
- Hardware drivers: Low-level code to communicate with keyboard, screen, storage devices
The Boot Process (Why ROM is Essential):
- Power on: Electricity reaches the motherboard
- ROM activates: CPU executes BIOS code stored in ROM (no operating system loaded yet!)
- POST runs: BIOS tests RAM, checks for keyboard, GPU, storage drives
- Boot device search: BIOS looks for bootable device (hard drive, USB, CD)
- Hand over control: BIOS loads bootloader, which then loads the operating system into RAM
Practice questions for RAM and ROM
Which of the following best describes RAM?
Explain why the BIOS must be stored in ROM rather than RAM.