What is BIOS?

In plain English

BIOS (say it "BYE-oss") stands for Basic Input/Output System. It's a tiny built-in program that lives on a chip on your computer's main board, and it's the very first thing that runs the instant you press the power button - before Windows even appears.

Think of it like the person who opens up a shop first thing in the morning: they unlock the doors, turn on the lights, check the till is there and the fridge is working, then hand over to the staff so the shop can actually trade. The BIOS does that wake-up-and-check routine for your PC - it makes sure the keyboard, screen, memory and hard drive are all present and working, then "hands over" to Windows to do the real work. On most newer Windows PCs this is technically called UEFI, but most people still just call it the BIOS.

Why it matters

You'll rarely touch the BIOS, and that's exactly how it should be - but it matters for two reasons. First, if it gets confused or its settings are wrong, your computer can fail to start at all, sometimes with a black screen or a beeping noise instead of Windows. Second, scam "support" callers and dodgy websites sometimes tell people to change BIOS settings - and the wrong change here can stop a perfectly healthy machine from booting. For a home user or a small business, that can mean a day lost and an unnecessary repair bill, so it's worth knowing what the BIOS is and treating it with respect.

What to do

• Leave it alone unless you know why you're in there. The BIOS is safe to ignore day to day - you almost never need to open it.
• Don't change settings just because a phone caller or pop-up tells you to. No genuine company cold-calls you to walk you through BIOS changes. If in doubt, hang up and ask someone you trust.
• If your PC won't start or beeps instead of loading Windows, note any message on the screen and get help rather than guessing - the cause is often simple.
• Keep Windows up to date. Manufacturer "firmware" or BIOS updates do exist, but they're best left to someone who knows the machine - a wrong one can do more harm than good.

How 365 Techies can help

If your Windows PC won't start, beeps, or someone's told you to change a setting you don't understand, we're a friendly local Dorset firm who'll take a look - remotely or in person - and tell you honestly what's going on.

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