Field Guide · hardware

Also known as: CPU, central processing unit, processor

The central processing unit (CPU) is the chip that carries out a program’s instructions — the part of computer hardware most often called the “brain.”1

One core: the instruction cycle Fetch Decode Execute cycles per second = clock speed (GHz) One package: many cores core core core core shared cache RAM data
A single core runs the same loop — fetch, decode, execute — billions of times a second; that rate is the clock speed. A modern CPU packs several cores that share a cache and pass data to and from separate RAM, so it can genuinely work on many tasks at once.

Overview

A CPU fetches instructions, decodes them, and executes them one after another, very fast. Modern CPUs contain several cores: each core is a self-contained processing unit, so a multi-core CPU can genuinely work on several tasks at the same time. This is what makes concurrency and parallel work practical.

Clock speed, measured in gigahertz (GHz), counts how many cycles a core runs per second. It is a rough guide to speed, not an absolute one — a newer 3 GHz core can outpace an older 4 GHz core because it does more useful work per cycle.

Where it fits

The CPU scales across the whole hardware spectrum. A microcontroller has a single tiny, low-power core; a desktop has a handful; a server may carry dozens. The CPU works hand in hand with RAM, which holds the data and instructions it is actively using.

Sources

  1. Central processing unit — Wikipedia, on CPU function, cores, and clock speed. ↩

See also

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