What Is BIOS/UEFI? The Software Behind Your PC's Power Button, Explained
The screen you sometimes glimpse at startup, what it is, what it does, and when you'd ever need it.
The software before the software
When you press your PC's power button, before Windows (or any OS) appears, a piece of low-level software runs first to get the machine going. That's the BIOS, or on modern computers, its successor UEFI. It's the firmware built into your motherboard that initializes your hardware and starts the boot process. Most people rarely see it, maybe a logo or a brief screen at startup, and never touch its settings. But understanding what it is demystifies how your computer actually starts up, and helps in the occasional situations where you do need to access it.
What BIOS/UEFI does
The BIOS/UEFI has a few core jobs, all happening in the moments after you hit power. It performs a self-check of your hardware (making sure the essential components are present and working), initializes and configures that hardware, and then locates and hands control to your operating system to boot up. It's the essential bridge between pressing the power button and your OS loading. It also stores low-level settings about your hardware and boot process. In short, it's the foundational firmware that wakes up the machine and gets everything ready for the operating system to take over.
BIOS vs UEFI
BIOS (Basic Input/Output System) is the traditional, decades-old firmware. UEFI (Unified Extensible Firmware Interface) is its modern replacement, found on essentially all recent computers, though people still often call it 'the BIOS' out of habit. UEFI does the same fundamental job but is more capable: it supports larger drives, faster boot times, better security features (like Secure Boot, which helps prevent malware from loading at startup), and often a nicer, mouse-friendly interface instead of the old text-only screens. For practical purposes, they play the same role in starting your PC; UEFI is just the newer, more advanced version you almost certainly have.
How to access it
You access the BIOS/UEFI setup by pressing a specific key immediately as the computer starts up, before the OS loads. The key varies by manufacturer, commonly Delete, F2, F10, F12, or Esc, and is often shown briefly on the startup screen ('Press [key] to enter setup'). You have to press it quickly during that early startup moment. On modern Windows, you can also reach UEFI settings through the advanced startup/recovery options (Settings, then System, then Recovery, then Advanced startup), which then reboots into the firmware. If you're not intentionally entering it, you'll never see these settings, and that's fine.
When you'd actually need it
Most people never need to touch the BIOS/UEFI, but a few situations call for it. Changing the boot order (to boot from a USB drive, for installing an operating system or running diagnostics). Enabling or checking hardware features (like virtualization support, or TPM and Secure Boot required by modern Windows). Troubleshooting hardware or boot problems. Adjusting settings when building or upgrading a PC. And occasionally updating the firmware itself. These are relatively uncommon, mostly enthusiast, troubleshooting, or setup tasks, which is why the BIOS/UEFI stays invisible in normal daily use.
A word of caution
The BIOS/UEFI controls fundamental hardware settings, so treat it with respect. Only change settings you understand and have a reason to change, incorrect changes can prevent your computer from booting or cause instability. If you enter it to do a specific task (like changing boot order), make that change and exit, rather than experimenting with settings you don't understand. Firmware updates, while sometimes beneficial, carry risk if interrupted, so do them carefully and only when needed. For the vast majority of users, the safest approach is simple: leave the BIOS/UEFI alone unless you have a specific, understood reason to enter it.
Related on Skillo
See also: What is TPM 2.0 and why Windows 11 needs it, How to boot Windows in Safe Mode (and why).
Sources
Published date reflects the original event date (2025-10-21). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
Written by
Skillo Staff
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