Memory and Storage
Understand how computers store data - from lightning-fast RAM to permanent storage.
What you'll learn:
- Why computers need primary storage (memory)
- The difference between RAM and ROM
- The purpose of RAM and ROM in a computer system
- What virtual memory is and why it's needed
- How cache memory speeds up your computer
- How data transfers between RAM and secondary storage
Specification Reference: 1.2.1 Primary Storage (Memory)
This topic covers the GCSE Computer Science specification requirements for understanding computer memory systems.
Key Concepts Overview
Primary Storage
Memory that the CPU can access directly. Includes RAM and ROM. Fast but limited in size.
RAM (Random Access Memory)
Volatile memory that stores data and programs currently in use.
- Volatile: Loses contents when power is off
- Read/Write: Can be changed
- Fast: Quick access times
- Stores: Running programs, open files, OS
ROM (Read Only Memory)
Non-volatile memory that stores permanent instructions.
- Non-volatile: Keeps contents when power is off
- Read Only: Cannot be changed (easily)
- Permanent: Set during manufacturing
- Stores: BIOS/boot instructions
Virtual Memory
Uses secondary storage as an extension of RAM when RAM is full.
- RAM becomes full
- Least-used data moved to hard drive (page file)
- When needed again, swapped back to RAM
- Called "paging" or "swapping"
Slower than RAM - causes "disk thrashing" if overused!
Cache Memory
Small, ultra-fast memory between CPU and RAM.
- Purpose: Stores frequently used data
- Speed: Faster than RAM
- Size: Very small (MB not GB)
- Levels: L1 (fastest), L2, L3
Memory Hierarchy
Computer memory is organised in a hierarchy - faster memory is smaller and more expensive:
RAM vs ROM Comparison
| Feature | RAM | ROM |
|---|---|---|
| Volatility | Volatile (loses data when power off) | Non-volatile (keeps data) |
| Read/Write | Can read and write | Read only (cannot change easily) |
| Speed | Fast | Slower than RAM |
| Size | Larger (4-64+ GB typical) | Smaller (few MB) |
| Purpose | Store running programs & data | Store boot instructions (BIOS) |
| Contents | Changes constantly | Permanent/rarely changes |
Learning Path
Follow these activities in order to master memory concepts.
1. Predict: Memory Scenarios
Predict what happens in different memory situations.
2. Study: How Memory Works
Step through how RAM, ROM, cache and virtual memory work together.
3. Investigate: Trace Memory Operations
Follow data as it moves through the memory hierarchy.
4. Modify: Arrange the Concepts
Put memory concepts and processes in the correct order.
5. Test: Knowledge Quiz
Check your understanding of memory and storage concepts.
Key Vocabulary
Primary Storage
Memory directly accessible by the CPU (RAM and ROM).
Secondary Storage
Permanent storage like hard drives and SSDs.
Volatile
Memory that loses its contents when power is switched off.
Non-volatile
Memory that retains its contents without power.
BIOS
Basic Input/Output System - stored in ROM, runs when computer starts.
Page File
Area on hard drive used for virtual memory.
Disk Thrashing
Excessive swapping between RAM and virtual memory, slowing the system.
Cache Hit/Miss
When requested data is (hit) or isn't (miss) found in cache.
Exam Tips
Common Exam Questions
- "Explain why a computer needs both RAM and ROM" (4 marks)
- "Describe how virtual memory works" (3 marks)
- "Explain the purpose of cache memory" (2 marks)
- "Compare RAM and ROM" (4 marks)
Key Points to Remember
- RAM = temporary, changeable, volatile
- ROM = permanent, fixed, non-volatile, stores BIOS
- Virtual memory = overflow for RAM, uses hard drive
- Cache = speeds up CPU access to frequently used data
- More RAM = less need for virtual memory = faster computer