That Blue Square Thing

AQA Computer Science GCSE

This page is up to date for the AQA 8525 syllabus for exams from 2022.

4.4 Computer Systems – Inside the CPU

thumbnail of CPU diagramAs part of his architecture, von Neumann described how the CPU would work. His design has a Central Control Part and a Central Arithmetic Part as the key components of the CPU.

Modern CPUs use these parts; they just have slightly different names and there's a bit more to it.

You need to know about some of the components inside the CPU:

PDF iconInside the CPU – slides from class

PDF iconInside the CPU – more detailed notes on the elements

If you need a diagram of the simplified structure of the CPU you can click on the thumbnail to get a larger version.

For more on how the CPU works to decode and execute instructions, see the Memory page. There's also more information on how registers work on that page.

For details on how to improve CPU performance, see the page about increasing CPU performance.

The Fetch–Decode–Execute Cycle

The CPU processes data. To do that it needs to move data and instructions around the computer system – using buses to move things stored in RAM into and out of the CPU's registers.

The ways it does this can be simplified down to the Fetch–Decode–Execute cycle.

Diagram of CPU components

PDF iconFetch–Decode–Execute – slides from class

The Fetch–Decode–Execute cycle is managed by the Control Unit element of the CPU. It involves the movement of data into and out of the CPU from main memory (RAM).