GCSE Computer Science: Systems Architecture Revision

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What does the CPU do?

Systems Architecture is a core part of GCSE Computer Science. Revise the key concepts and common mistakes below, then lock them in with the free games.

Key concepts

Von NeumannStores data and instructions in same memory.

CPUCentral processing unit — executes instructions.

ALUArithmetic logic unit — does maths and logic.

CUControl unit — directs the CPU's actions.

RAMMain memory holding programs and data in use.

I/OInput and output devices, e.g. keyboard, screen.

FetchGet the next instruction from memory.

DecodeWork out what the instruction means.

ExecuteCarry out the instruction.

PCProgram counter — holds next instruction's address.

MARMemory address register — address being accessed.

MDRMemory data register — data being transferred.

Clock speedHow many cycles a CPU does per second.

GHzGigahertz — 1,000,000,000 cycles per second.

What your exam board covers

Where Systems Architecture sits in each exam board's specification. Tap a board to see what it lists.

AQAComputer systemsSpec 8525

Hardware and software
Boolean logic
Systems architecture and the CPU
Memory and storage

Source: AQA GCSE Computer Science (8525) specification — Subject content, accessed 23 June 2026.

OCRSystems architectureSpec J277

Part of: Component 1 — Computer systems

Source: OCR GCSE (9–1) Computer Science (J277) specification, accessed 23 June 2026.

Learn Systems Architecture step by step

Free interactive mini-lessons: short screens, worked examples and quick checks. Pick your exam board:

Other boards:Edexcel Cambridge IGCSE

Common mistakes to avoid

Questions where students often pick the tempting wrong answer — make sure you know the right one:

What does the CPU do?✗ Permanently stores all the computer's files. ✓ Processes instructions (fetch–decode–execute).

How do RAM and storage differ?✗ They are the same thing. ✓ RAM is fast, volatile working memory; storage keeps data without power.

Practise Systems Architecture — free games

Test yourself with these quick revision games for this topic:

▶ Two Truths, One Lie ▶ Reveal Race ▶ Connections Grid ▶ Falling Words ▶ Word Web

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Systems Architecture

Key concepts

What your exam board covers

Common mistakes to avoid

Practise Systems Architecture — free games

More GCSE Computer Science topics