You've probably seen it. Maybe your laptop ran out of battery and died mid-update, or perhaps you were just mash-tapping keys trying to get a stubborn PC to wake up. Suddenly, the familiar Windows or macOS logo is gone. Instead, you're staring at a terrifying, low-resolution screen filled with blocky text and settings that look like they belong in 1992.
Welcome to the BIOS.
Most people ignore it. Honestly, that’s usually a good idea because poking around in there without a plan is a great way to turn a $2,000 gaming rig into a very expensive paperweight. But if you've ever wondered what is BIOS and why your computer literally cannot breathe without it, you're in the right place. It’s the most fundamental piece of software you own, yet it’s technically not even on your hard drive.
The Ghost in the Machine: Defining the BIOS
BIOS stands for Basic Input/Output System. It is the first thing that "wakes up" when you hit the power button. Before your processor knows how to talk to your RAM, and way before your computer realizes it has an operating system like Windows 11 installed, the BIOS is running the show.
Think of it as the "involuntary nervous system" of your computer.
Just like you don't have to remind your heart to beat or your lungs to expand, your motherboard uses the BIOS to handle the basic survival tasks of a computer. It identifies the hardware. It checks if the fans are spinning. It makes sure the CPU isn't melting. If the BIOS doesn't give the "all clear," your computer isn't going anywhere.
Where does it actually live?
It’s not on your SSD. If you wiped your entire hard drive right now, the BIOS would still be there. It lives on a small non-volatile ROM chip soldered directly onto the motherboard. This is why you can still access these settings even if your boot drive is completely corrupted or missing.
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What Does the BIOS Actually Do?
There are four main jobs this ancient-looking software handles every single time you boot up.
- POST (Power-On Self-Test): This is the diagnostic phase. The BIOS checks your hardware—keyboard, mouse, memory, storage—to ensure everything is working. If you’ve ever heard your computer make a weird "beep" sound when starting, that’s a POST code telling you something is wrong.
- Bootstrap Loader: This is the hand-off. The BIOS looks for a valid operating system (like Windows, Linux, or macOS) on your drive and hands over control to it.
- BIOS Drivers: These are low-level drivers that give the computer basic control over your hardware before the "real" drivers in your OS take over.
- CMOS Setup: This is the menu you see when you "enter the BIOS." It’s where you change things like the system clock or which drive should boot first.
A quick note on CMOS
People often use "BIOS" and "CMOS" interchangeably. They aren't the same. The BIOS is the program; the CMOS (Complementary Metal-Oxide-Semiconductor) is the physical memory chip that stores your settings (like the date and time). This is powered by a little coin-cell battery on your motherboard. If that battery dies, your computer "forgets" what time it is every time you unplug it.
The Big Shift: BIOS vs. UEFI
If you’ve bought a computer in the last decade, you technically don't have a traditional BIOS. You have UEFI (Unified Extensible Firmware Interface).
Standard BIOS is old. It dates back to the CP/M operating system in 1975. Because of its age, it has massive limitations. It can’t boot from hard drives larger than 2.2 Terabytes, and it operates in 16-bit mode, which is painfully slow.
UEFI is the modern successor. It’s faster, it supports massive drives, and—most importantly for many—it allows you to use a mouse in the settings menu. Old-school BIOS required you to navigate using only a keyboard, which felt like trying to program a VCR in the dark.
Why do we still call it BIOS?
Habit. Even though modern motherboards from ASUS, MSI, or Gigabyte use UEFI, the manufacturers still label the menus as "BIOS" because that's what everyone knows to look for.
Why Would You Ever Need to Enter the BIOS?
For most users, the answer is "never." But if you're a tinkerer or you're trying to fix a broken PC, the BIOS is your best friend.
- Changing Boot Order: If you want to install a new operating system from a USB drive, you have to tell the BIOS to look at the USB stick before it looks at the internal hard drive.
- Overclocking: This is where enthusiasts go to make their CPU run faster than the factory settings. It involves changing voltages and clock speeds. Do it wrong, and you’ll smell smoke.
- Hardware Monitoring: If your computer is crashing, you can check the BIOS to see the real-time temperature of your processor.
- Enabling Virtualization: If you want to run a Virtual Machine (VM) for work or use the Windows Subsystem for Android, you often have to toggle a setting called "Intel VT-x" or "AMD-V" inside the BIOS.
The TPM 2.0 Drama
When Windows 11 launched, millions of people suddenly had to learn what a BIOS was. Microsoft required a feature called TPM 2.0 (Trusted Platform Module) for security. Many PCs had this hardware, but it was turned off by default in the BIOS. Suddenly, everyone was Googling "how to enter BIOS" just to click one single toggle so they could upgrade their software.
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Security Risks: Can a BIOS get a virus?
Unfortunately, yes. And they are terrifying.
Because the BIOS starts before your antivirus software, a "rootkit" or "bootkit" that infects the BIOS can be nearly impossible to remove. You could format your hard drive a hundred times and the virus would still be there, waiting to re-infect your system as soon as you reinstall Windows.
This is why modern UEFI systems have Secure Boot. It’s a feature that checks the "signature" of the operating system to make sure it hasn't been tampered with. It’s also why you should be very careful about downloading "BIOS updates" from anywhere other than the official manufacturer's website.
How to Access Your BIOS (It’s Frustrating)
There is no universal way to get in. Every manufacturer decided to pick a different key.
Usually, you have to spam a specific key on your keyboard the very second you see the manufacturer's logo after turning the power on.
- Dell: F2 or F12
- HP: F10 or Esc
- ASUS: Del or F2
- Lenovo: F1, F2, or the tiny "Novo" button on the side of some laptops
If you have a modern Windows PC that boots too fast for you to hit a key, you can actually get there through Windows. Go to Settings > System > Recovery > Advanced Startup, and then choose Troubleshoot > Advanced options > UEFI Firmware Settings. Much easier than mashing the Delete key like a madman.
Flashing the BIOS: The Scariest 5 Minutes in Tech
You might see an update available for your BIOS. This process is called "flashing."
Unlike a Windows update, if a BIOS update fails—say, because your power goes out—your motherboard is "bricked." It essentially forgets how to be a computer. It won't even know how to turn on the screen to tell you it's broken.
Should you update?
Only if you have to. If your computer is running fine, leave it alone. The only reasons to flash a BIOS are:
- You're installing a newer CPU that the motherboard doesn't recognize yet.
- You're experiencing a major hardware bug that the update specifically fixes.
- There is a critical security vulnerability (like the "Spectre" or "Meltdown" flaws from a few years ago).
Actionable Tips for Managing Your BIOS
If you find yourself staring at those blue and grey menus, keep these rules in mind so you don't break anything.
- Take a photo first. Before you change any setting, take a picture of the screen with your phone. If the computer won't boot afterward, you'll know exactly what the original setting was.
- Look for "Load Optimized Defaults." Every BIOS has this option. If you messed something up and the PC is acting weird, selecting this will reset everything to the factory-safe settings.
- Watch your voltages. If you're experimenting with overclocking, never move voltage sliders unless you've read a specific guide for your exact CPU. High voltage kills silicon instantly.
- Enable XMP/DOCP. If you bought high-speed RAM, it often runs at a slower "safe" speed by default. You usually have to go into the BIOS and enable an XMP (Intel) or DOCP (AMD) profile to actually get the speed you paid for.
Understanding the BIOS isn't just for IT professionals. It’s about knowing how the foundation of your digital life works. It’s the bridge between the physical metal of your motherboard and the pixels of your operating system. Keep it updated when necessary, respect its power, and maybe—just maybe—don't touch the "CPU Voltage" slider unless you're feeling particularly brave.
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Next Steps for You
Check your current BIOS version by typing msinfo32 into your Windows search bar and looking at "BIOS Version/Date." If it's more than three years old and you're having stability issues, head to your motherboard manufacturer's support page to see if a critical update is waiting for you. Just make sure the weather is clear and your power is stable before you hit that "Update" button.