GCSE Computer Science: Understanding Computer Architecture

Computer architecture is one of those GCSE Computer Science topics that sounds intimidating but is actually very logical once you can see how the parts fit together. At its heart, it’s about how a computer is organised internally and how data moves around the system.

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🧠 The Big Picture: The Von Neumann Architecture

Most GCSE courses are based on the Von Neumann architecture, a model where:

• Data and instructions share the same memory

• A single CPU processes everything

• Information moves via a system of buses

This design explains why computers can multitask — but also why bottlenecks can occur when too much data needs to move at once.

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⚙️ The CPU: The Engine of the Computer

The Central Processing Unit (CPU) is made up of three key parts:

• Control Unit (CU) – directs operations and manages the fetch–decode–execute cycle

• Arithmetic Logic Unit (ALU) – carries out calculations and logical decisions

• Registers – tiny, ultra-fast memory locations holding current instructions and data

GCSE tip: Registers are faster than RAM but far smaller.

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🔄 The Fetch–Decode–Execute Cycle

Every program runs as a repeating loop:

1. Fetch – get the instruction from memory

2. Decode – work out what the instruction means

3. Execute – carry out the instruction

This cycle is central to many exam questions and is well worth practising with diagrams.

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🧵 Buses: The Data Motorways

Three buses connect components:

• Data bus – transfers actual data

• Address bus – specifies where data is

• Control bus – sends control signals

Exam insight: The width of a bus affects performance.

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💾 Memory: RAM vs ROM

• RAM – volatile, temporary, fast (programs in use)

• ROM – non-volatile, permanent (start-up instructions / BIOS)

Students often confuse volatile with erasable — volatile simply means data is lost when power is off.

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⌨️ Input and Output Devices

• Input devices send data into the system (keyboard, mouse, sensors)

• Output devices send data out (screen, printer, speakers)

Linking inputs and outputs back to the CPU and memory helps students understand the whole system, not just isolated parts.

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🎓 Why This Topic Matters

Computer architecture underpins:

• Programming performance

• Why some computers feel faster than others

• Later topics like secondary storage, networks, and operating systems

It’s not just exam theory — it explains how real computers actually work.