Technology
How does a CPU work?
A CPU works by fetching instructions from memory, decoding what each one means, and executing it — billions of times a second. It repeats this fetch-decode-execute cycle on simple operations like add, compare, and move data that together run every program on your device.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a CPU works.
Step by step
- 1It runs a constant 'fetch-decode-execute' cycle: get an instruction, work out what it means, carry it out.
- 2A clock keeps everything in step, ticking billions of times per second (gigahertz).
- 3It only does simple operations — arithmetic, comparisons, moving data — but at staggering speed.
- 4Multiple 'cores' let it run several streams of instructions at once.
- 5On-chip memory called cache keeps frequently used data close, so the CPU isn't left waiting on slower main memory.
Frequently asked questions
- What does clock speed (GHz) mean?
- It is how many cycles the CPU runs per second — 3 GHz is three billion cycles a second. More cycles can mean more work, though design and core count matter just as much.
- What is the difference between a CPU and a GPU?
- A CPU has a few powerful cores great at varied, sequential tasks; a GPU has thousands of simpler cores built to do the same operation on lots of data at once.
- What are cores?
- Each core is an independent processing unit. More cores let the CPU handle multiple tasks or threads truly in parallel.