The CPU

About this lab: The CPU

Interactive simulation for Cambridge IGCSE Computer Science 0478 topic 3.1 and AS & A Level 9618 topic 4: explore the Von Neumann CPU, its registers and buses, step through the fetch-decode-execute cycle with register transfer notation, compare cores, cache and clock speed, see embedded systems, trace assembly language programs with the 9618 instruction set, compare addressing modes and handle interrupts by priority.

IGCSE Computer Science 0478, topic 3.1, and A-Level 9618, topic 4. Von Neumann architecture, the fetch-decode-execute cycle with register transfer notation, cores, cache and clock speed, instruction sets and embedded systems, then assembly language, addressing modes and interrupts for A-Level.

The CPU is a free, browser-based simulation for Cambridge IGCSE Computer Science 0478 (topic 3 Hardware, section 3.1 Computer architecture). The same lab serves both Cambridge IGCSE Computer Science 0478 and AS & A Level Computer Science 9618; tabs marked A-Level go beyond the IGCSE syllabus. The course is assessed in Paper 1 (Computer Systems), Paper 2 (Algorithms, Programming and Logic). Syllabus for examination in 2026-2028. There are 7 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.

Syllabus coverage

• 3.1 Computer architecture. Lessons: The CPU and Von Neumann architecture, The fetch-decode-execute cycle, Cores, cache and clock speed, Instruction sets and embedded systems.
• 9618 4.1 Central Processing Unit (CPU) Architecture. Lessons: The Von Neumann model and registers, Buses, ports and processor performance, The fetch-execute cycle in register transfer notation.
• 9618 4.2 Assembly Language. Lessons: Assembly language and the two-pass assembler, Addressing modes, Tracing an assembly language program.
• 9618 4.3 Bit manipulation. Lessons: Shifts, masks and bit manipulation.

Full syllabus map: IGCSE Computer Science 0478 topic 3 and A Level Computer Science 9618 topic 4.

How to use this simulation

1. 1. Von Neumann architecture.
2. 2. Fetch-decode-execute.
3. 3. Cores, cache, clock.
4. 4. Instruction sets, embedded systems.
5. 5. Assembly language.
6. 6. Addressing modes.
7. 7. Interrupts.
8. The buttons at the end of the tab strip give the scene the whole window (Full screen, Hide controls) and, on a dark stage, a projector-friendly palette (Light scene). Many scenes also have drag handles: drag them to change the set-up directly.

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