The CPU — Computer Architecture | IGCSE Computer Science

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 7% of your exam marks.

stable

Low

Stable7%

The fetch-decode-execute cycle and von Neumann architecture are tested almost every year.

The Central Processing Unit (CPU) is the part of a computer that runs every program. It is the chip that takes a stream of binary instructions and acts on them, one at a time, billions of times per second.

The job of the CPU is to fetch, decode and execute instructions. Everything else a computer does (showing text on a screen, playing audio, running a game, opening a web page) is built from these three steps.

The CPU sits between the input devices (keyboard, mouse, sensors) that feed it data, and the output devices (monitor, speakers, printer) that show the results. Memory (RAM) and storage (SSD or hard drive) hold the data and instructions the CPU works on.

CPU and microprocessor

These two terms get confused often:

The CPU is the part of a chip that does the actual fetching, decoding and executing.
A microprocessor is the physical chip itself. It contains the CPU, and often other circuitry such as memory controllers, cache, and input/output interfaces.

A modern laptop has one microprocessor chip containing several CPU cores plus a lot of supporting hardware. For exam purposes, treat "CPU" as the logical processing unit and "microprocessor" as the physical chip.