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Definition ELI9-o-meter 2 min read

What Is the CPU?

People shopping for a computer fixate on the CPU with no idea what it is, only that a bigger number costs more. It’s the brain of the machine, and it maps neatly onto your own memory.

Meeke September 3, 2026

When people shop for a computer, they fixate on the CPU and often have no idea what it is, only that a bigger number costs more. It is worth knowing, because the CPU is genuinely the heart of the thing, or rather, the head.

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In plain English

The CPU, or Central Processing Unit, is the brain of the computer. It does the actual thinking, and how good it is decides how fast that thinking happens.

The brain, and how the rest of the head works

The CPU is the brain, and it is also how fast that brain can think. Everything the computer does, every calculation, every click you make, runs through it. A faster CPU is a quicker mind.

The nice thing is that the rest of the computer maps neatly onto how your own memory works, once you see the CPU as the brain:

  • Your disk drive is long-term memory: everything you have stored and can pull up later, your version of a filing cabinet full of everything you know.
  • Your RAM is short-term memory: the handful of things you are actively thinking about right this second.
  • The CPU decides both how quickly you think and how much you can juggle at once before you run out of room and have to start jotting things on Post-it notes. Those notes, the overflow your computer scribbles down when short-term memory fills up, are the page file, a cousin of the cache.

The CPU is the brain. The disk is your long-term memory, RAM is your short-term memory, and the CPU sets how fast and how much you can think at once.

Side note

This is why a computer can feel slow for two completely different reasons. A weak CPU is a slow thinker, no way around it. But even a fast brain bogs down when its short-term memory is full and it is constantly scribbling Post-its. That is why adding RAM can perk up a sluggish machine even when the CPU is perfectly fine. Different bottleneck, different fix.

Too long, didn’t read

  • The CPU is the computer’s brain, and how fast it thinks.
  • The disk is long-term memory; RAM is short-term memory.
  • The CPU sets how quickly and how much you can think at once.
  • When short-term memory fills, the computer writes Post-its (the page file), which slows things down.

Meeke

CEO (Chief Explanation Officer) · Like I'm 9

A real person behind a cartoon apple. In tech since elementary school, back when serious storage meant magnetic tape. Explaining it in plain English: no jargon, no judgment, no sponsors. The videos use an AI voice so I can keep my identity out of it.

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