Edexcel 1CP2 · GCSE Computer Science · ~13 min read · 🔒 Pro
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RAM (Random Access Memory)
RAM is the computer's main memory — it holds the operating system, currently running programs, and data being processed.
Volatile — loses all data when power is off
Read/write — data can be read and changed
Fast access — much faster than secondary storage
More RAM = more programs can run simultaneously without slowdown
ROM (Read-Only Memory)
ROM stores the BIOS/firmware — the boot instructions the computer needs to start up.
Non-volatile — retains data without power
Read-only — cannot be changed by normal programs
Contains the POST (Power-On Self Test) and instructions to load the OS
RAM vs ROM
Feature
RAM
ROM
Volatile?
Yes (loses data when off)
No (persistent)
Read/Write?
Read and write
Read only
Contents
OS, programs, current data
Boot instructions (BIOS)
Typical size
4 GB – 64 GB
Very small (few MB)
Virtual Memory
When RAM is full, the OS creates virtual memory by using a section of the hard drive/SSD as temporary RAM.
The OS moves inactive pages from RAM to secondary storage (called paging or swapping)
Allows the computer to run more programs than RAM can hold
Disadvantage: secondary storage is much slower than RAM, so virtual memory causes noticeable slowdown
Very heavy reliance on virtual memory is called thrashing — the system becomes very slow
Memory Hierarchy
Type
Speed
Size
Volatile?
CPU Registers
Fastest
Tiny (bytes)
Yes
Cache (L1–L3)
Very fast
KB–MB
Yes
RAM
Fast
GB
Yes
Virtual memory (HDD/SSD)
Slow
GB–TB
No
Secondary storage
Slowest
GB–TB
No
Exam tip: A very common Edexcel question is "Explain what happens when the computer runs out of RAM". Answer: the OS uses part of the hard drive as virtual memory (paging), moving inactive RAM contents to secondary storage. This works but is slower because hard drives are much slower than RAM.
⚠️ Common Mistakes
Confusing RAM (volatile, read/write) with ROM (non-volatile, read only)
Thinking virtual memory is the same as RAM — it's secondary storage acting as overflow
Saying ROM stores user files — ROM only contains firmware/boot instructions
Forgetting that virtual memory is SLOWER than RAM
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Worksheet — 3.1c Memory
8 Edexcel-style questions · instantly marked
Q1State what is meant by 'volatile' memory.[1]
✅ Mark scheme
Volatile memory loses its contents when power is removed [1].
Q2State two differences between RAM and ROM.[2]
✅ Mark scheme
Any two: RAM is volatile, ROM is non-volatile [1]; RAM is read/write, ROM is read-only [1]; RAM stores current programs/data, ROM stores boot instructions/BIOS [1].
Q3What is stored in ROM?[1]
✅ Mark scheme
ROM stores the BIOS/firmware — the boot instructions needed to start the computer [1].
Q4Explain what happens when a computer runs out of RAM.[3]
✅ Mark scheme
The OS creates virtual memory [1]; it moves inactive pages from RAM to secondary storage (paging/swapping) [1]; this is slower than RAM so performance decreases [1].
Q5What is 'thrashing' in relation to virtual memory?[2]
✅ Mark scheme
Thrashing occurs when the system is constantly swapping data between RAM and virtual memory [1]; this causes severe slowdown as the hard drive is much slower than RAM [1].
Q6State one advantage of having more RAM.[1]
✅ Mark scheme
More programs can run simultaneously without the need for virtual memory [1]. Accept: faster performance / reduced reliance on virtual memory.
Q7Put the following in order from fastest to slowest: RAM, Virtual memory, CPU Registers, Cache.[2]
✅ Mark scheme
CPU Registers → Cache → RAM → Virtual memory [2 marks for all correct, 1 mark for two or three correct positions].
Q8Why is ROM non-volatile? What would happen if it were volatile?[2]
✅ Mark scheme
ROM must retain boot instructions without power [1]; if volatile, the boot instructions would be lost when the computer is switched off, and the computer would not be able to start [1].
Topic Quiz
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Mini Test — RAM, ROM & Virtual Memory
Timed exam-style test.
⏱10:00
Section A — Multiple Choice [5 marks]
Q1RAM is:[1]
Q2ROM stores:[1]
Q3Virtual memory is:[1]
Q4What is 'thrashing'?[1]
Q5From fastest to slowest: CPU Registers, Cache, RAM, Virtual Memory — which is correct?[1]
Section B — Short Answer
Q6Explain what happens when a computer runs out of RAM. Include what virtual memory is and its disadvantage.[3]
Mark schemeThe OS creates virtual memory [1]; uses part of secondary storage (HDD/SSD) as overflow RAM [1]; inactive pages are swapped out of RAM to secondary storage [1]; this causes slowdown because secondary storage is much slower than RAM [1].
Q7State two differences between RAM and ROM.[2]
Mark schemeRAM is volatile / ROM is non-volatile [1]; RAM is read/write / ROM is read-only [1].