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The Fetch-Execute Cycle: What’s Your Computer Actually Doing?

Tom Scott | November 13, 2025



The fetch-execute cycle is the basis of everything your computer or phone does. This is literally The Basics. • Sponsored by Dashlane —try 30 days for free at: https://www.dashlane.com/tomscott

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MORE BASICS: https://www.youtube.com/playlist?list=PL96C35uN7xGLLeET0dOWaKHkAlPsrkcha

MINOR CORRECTIONS:
In the graphics, “programme” should be “program”.
I say “Mac instead of PC”; that should be “a phone instead of a PC”.
And most importantly, I say “every sixth cycle”: that should be “every ninth”.
Fortunately, none of these materially affect the content of the video!

Written with Sean Elliott https://twitter.com/SeanMElliott/
Directed by Tomek
Graphics by Mooviemakers https://www.mooviemakers.co.uk/
Audio mix by Haerther Productions https://haerther.net/

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Written by Tom Scott

Comments

This post currently has 36 comments.

  20. @petergrimshaw492

    November 13, 2025 at 7:13 pm

    Thanks Tom great.
    I was at Uni struggling years ago with coding but gave up because I could not get my head around what was going on in the background.
    I want to build a really slow computer using gravity to prove I understand the principles.
    This has been a great help!

  28. @faxfir1027

    November 13, 2025 at 7:13 pm

    I think the reading metaphor creates many problems when it comes to understanding how the CPU works. I believe, and correct me if I'm wrong, that the CPU's genetic makeup contains logic circuits that are like interlocking machines represented by each instruction; it's like a labyrinth of data buses and electronic logic circuits. Rather than reading, circuits are switched on and off thousands of times per second.

  30. @raghavad.g7541

    November 13, 2025 at 7:13 pm

    Greetings, about the Fetch-Execute cycle, doesn't the PC increment its value when the data is getting decoded in the CIR. Is it for the sake of simplicity that this has been neglected or am I wrong. A clarification would be helpful.

  34. @omaryarali7805

    November 13, 2025 at 7:13 pm

    An amazing feature of compilers is their ability to optimize high-level code into machine code that is often remarkably efficient and can rival the performance of human-written assembly in many cases.

  35. @DexieTheSheep

    November 13, 2025 at 7:13 pm

    i don't know if you're using a limiter/compressor cranked all the way up or if you're just layering a snap sound effect over the real one, but those sound so clean and satisfying

Comments are closed.

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