The CPU
The central processing unit is the brain of the computer that carries out instructions in the fetch-decode-execute cycle.
▶ Interact
Play with the controls to see the idea in action.
📘 Learn
The central processing unit is the brain of the computer that carries out instructions in the fetch-decode-execute cycle.
- Fetch gets an instruction from memory
- Decode works out what it means
- Execute carries it out
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is The CPU?
Within Computer Science, which covers algorithms, programming, data, networks, hardware and safe, responsible use of technology, this topic explains The CPU. Computing topics explain how software, hardware and data work, with diagrams and models that show each step in order.
Check that you can explain The CPU in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding The CPU helps you design, test and explain programs, websites and systems, from small projects to exam questions.
The CPU in detail
The central processing unit (CPU) is the "brain" of the computer, carrying out program instructions. It includes the arithmetic logic unit (ALU), which performs calculations and logical comparisons, the control unit (CU), which directs the flow of data and instructions, and registers, tiny very fast storage locations. Cache memory holds frequently used data close to the CPU.
Performance depends on clock speed (measured in gigahertz, billions of cycles per second), the number of cores (each can work on a separate task) and cache size. Modern CPUs contain billions of transistors. Embedded systems use small, specialised processors.
How the interactive helps you understand The CPU
Click a step, or use the Previous and Next buttons, to move through the sequence one stage at a time. Auto-play moves on for you.
Before you change anything, predict the result. Then change one value at a time and check whether your prediction was right. This is a quick way to build a correct mental model of The CPU.
Real-life uses and examples
- Apply The CPU when you design a small program, website or spreadsheet.
- Explain The CPU to someone new to computing by comparing it to a familiar process.
- Trace through a process that uses The CPU to check what it does step by step.
Common mistakes to avoid
- Testing only the normal case and forgetting the edge cases.
- Using the term without being able to say what the computer actually does.
- Learning the definition without testing it. Use the quiz and the interactive to check that you can apply the idea.
Frequently asked questions about The CPU
What is The CPU?
The central processing unit is the brain of the computer that carries out instructions in the fetch-decode-execute cycle.
What are the most important points about The CPU?
The main points are: Fetch gets an instruction from memory; Decode works out what it means; Execute carries it out.
Why is The CPU useful?
Understanding The CPU helps you design, test and explain programs, websites and systems, from small projects to exam questions.
How can I practise The CPU?
Open the interactive at the top of this page and change the controls one at a time. Predict the result before each change, then take the three-question quiz. A score of two or more marks the topic as complete on this device.
Which topics are related to The CPU?
Related topics in Computer Science include Secondary Storage, Binary Numbers, Binary Arithmetic.