The Fetch-Decode-Execute Cycle
The fetch-decode-execute cycle is the repeated process in which the CPU fetches an instruction, decodes it and executes it.
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The fetch-decode-execute cycle is the repeated process in which the CPU fetches an instruction, decodes it and executes it.
- The program counter holds the next address
- The ALU does calculations
- The control unit directs the process
🧠 Quick quiz
Three questions. Score 2 or more to complete the topic.
What is The Fetch-Decode-Execute Cycle?
Within Computer Science, which covers algorithms, programming, data, networks, hardware and safe, responsible use of technology, this topic explains The Fetch-Decode-Execute Cycle. 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 Fetch-Decode-Execute Cycle in your own words and give one example from everyday life. If you can do that, you have understood the core idea.
Understanding The Fetch-Decode-Execute Cycle helps you design, test and explain programs, websites and systems, from small projects to exam questions.
The Fetch-Decode-Execute Cycle in detail
The fetch-decode-execute cycle is how the CPU runs programs, repeating billions of times a second. In the fetch stage, the instruction whose address is held in the program counter is copied from memory into the CPU. In the decode stage, the control unit works out what the instruction means.
In the execute stage, the instruction is carried out, such as an addition by the ALU or loading data from memory. The program counter is then updated to point to the next instruction, and the cycle repeats. Jumps and branches change the counter. This simple loop underlies all software, from calculators to games.
How the interactive helps you understand The Fetch-Decode-Execute Cycle
Watch the cycle in the interactive. Use any sliders or buttons it offers to change the values and see how the cycle responds.
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 Fetch-Decode-Execute Cycle.
Real-life uses and examples
- Trace through a process that uses The Fetch-Decode-Execute Cycle to check what it does step by step.
- Recognise The Fetch-Decode-Execute Cycle in an app or device you use every day.
- Apply The Fetch-Decode-Execute Cycle when you design a small program, website or spreadsheet.
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 Fetch-Decode-Execute Cycle
What is The Fetch-Decode-Execute Cycle?
The fetch-decode-execute cycle is the repeated process in which the CPU fetches an instruction, decodes it and executes it.
What are the most important points about The Fetch-Decode-Execute Cycle?
The main points are: The program counter holds the next address; The ALU does calculations; The control unit directs the process.
Why is The Fetch-Decode-Execute Cycle useful?
Understanding The Fetch-Decode-Execute Cycle helps you design, test and explain programs, websites and systems, from small projects to exam questions.
How can I practise The Fetch-Decode-Execute Cycle?
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 Fetch-Decode-Execute Cycle?
Related topics in Computer Science include Operating Systems, Converting Binary and Decimal, Text, Images and Sound as Data.