What is CPU (processor)?

In plain English

The CPU — short for Central Processing Unit, and often just called the "processor" — is the part of your computer that does the actual thinking. Every time you open an email, click a link or type a document, the CPU works out what needs to happen and makes it happen, step by step, billions of times a second.

Think of it like the chef in a kitchen. The ingredients and recipes are stored elsewhere (on your hard drive or SSD), and the worktop where the chef lays things out is your RAM. But it's the chef — the CPU — who reads each order and does the cooking. A faster, more capable chef gets more meals out, quicker. On a Windows PC or an Android phone, the CPU is a small chip tucked away inside; you'll never see it, but you feel it every time the machine responds.

Why it matters

The CPU is one of the biggest reasons a computer feels fast or frustratingly slow. If your PC takes an age to start up, stalls when you have a few browser tabs open, or chugs during video calls, an older or weaker processor is often part of the picture. For a small business, a sluggish machine quietly costs you time every single day. The good news: a slow computer isn't always the CPU's fault — too little RAM or an old-fashioned hard drive are just as common, and far cheaper to fix — so it's worth knowing what's actually holding things back before spending money.

What to do

• Don't panic about jargon like "i5" or "Snapdragon". You don't need to memorise model names. What matters is whether the computer keeps up with what you actually do.
• Try the cheap fixes first. A slow machine is very often cured by adding RAM or swapping an old hard drive for an SSD — you may not need a whole new computer.
• Restart regularly. Giving Windows a proper restart frees up the processor and often perks things up straight away.
• When buying, match the CPU to the task. Everyday email, web and Office work needs far less than photo or video editing. Don't overpay for power you'll never use — or under-buy and regret it.
• Ask before you replace. A quick check can tell you whether the processor really is the bottleneck, so you don't spend on the wrong thing.

How 365 Techies can help

If your Windows PC feels slow and you're not sure whether it's the processor, the memory or the hard drive, we'll happily take a look and tell you honestly — in plain English — whether it's worth upgrading or replacing.

Related: RAM · SSD · Hard drive · Operating system — or browse the full A–Z jargon buster.