What the BIOS is and why you might need to open it

The BIOS (Basic Input/Output System) is a program that runs before your operating system loads. It controls how your computer's hardware — the processor, memory, storage drives — talks to Windows or macOS. Most of the time you never need to touch it. But if you're troubleshooting a slow computer, changing boot order to run a diagnostic tool, or adjusting power settings, you'll need to get in.

Opening the BIOS is not the same as opening a regular program. You can't click an icon on your desktop. Instead, you restart your computer and press a specific key at exactly the right moment — before Windows or macOS starts. The key varies by manufacturer: Dell uses F2, HP and Lenovo often use F10 or Del, and some older machines use F1 or Esc. If you're not sure which key your computer uses, check the manufacturer's support page or look for a message on the startup screen that says "Press [key] to enter Setup".

Key Takeaways

  • You enter the BIOS by restarting your computer and pressing a specific key (usually F2, F10, or Del) before the operating system loads.
  • The correct key depends on your computer's manufacturer — Dell, HP, Lenovo, and others each use different keys.
  • Once inside, you navigate using arrow keys and Enter; do not make changes unless you know what each setting does.
  • The most common reason to open the BIOS is to change the boot order so your computer starts from a USB drive or external device.
  • If you make a mistake, you can usually reset the BIOS to factory defaults without damaging your computer.

How to open the BIOS on a Windows computer

Restart your computer completely. As it powers back on, watch the screen carefully. Within the first few seconds, before the Windows logo appears, you'll see a message like "Press F2 to enter Setup" or "Press Del for BIOS Settings". Press that key repeatedly — don't hold it down, tap it several times per second — until the BIOS screen appears. If you miss the window, the computer will boot into Windows normally and you'll have to restart and try again.

If you don't see a message on startup, look up your computer's manufacturer and model number. You can find the model on a sticker on the bottom or back of the machine, or in Windows by right-clicking "This PC" and selecting "Properties". Then search "[manufacturer] [model] enter BIOS" — the manufacturer's support page will tell you the correct key.

On newer Windows computers, there's an alternative: go to Settings, select "System," then "Recovery," and click "Restart now" under "Advanced startup." When the menu appears, choose "Troubleshoot," then "Advanced options," then "UEFI Firmware Settings." This will restart your computer directly into the BIOS without the timing pressure.

How to open the BIOS on a Mac

Shut down your Mac completely. Turn it back on and when ready press and hold the Command and R keys together until you see the Apple logo or a spinning globe. This takes you to Recovery Mode, not the BIOS directly — Macs don't have a traditional BIOS the way Windows computers do. Instead, they use firmware called EFI or Apple Silicon firmware.

From Recovery Mode, you can restart into Safe Mode, run Disk Utility to check your drive, or access other troubleshooting tools. If you need to change low-level hardware settings on an Intel Mac, go to the Utilities menu and select "Firmware Password Utility." On newer Macs with Apple Silicon chips, hardware settings are much more limited and rarely need adjustment by the user.

Navigating the BIOS menu and finding common settings

Once you're in the BIOS, you'll see a dark screen with white or blue text organized into tabs or sections. Use the arrow keys on your keyboard to move between options. Press Enter to select or change a setting. Do not use your mouse — the BIOS predates modern mice and doesn't respond to them.

Common sections you'll see include "Main" (basic system information), "Advanced" (processor and memory settings), "Boot" (the order in which your computer tries to start from different devices), "Security" (passwords and drive locks), and "Exit" (where you save and leave). The "Boot" section is where most people go when they need to change which device the computer starts from — for example, to run a diagnostic tool from a USB drive.

If you're not sure what a setting does, don't change it. Changing the wrong setting can prevent your computer from starting. Most BIOS screens show a description of the highlighted option on the right side or bottom of the screen — read that before making any change.

Changing the boot order to start from a USB drive

The boot order tells your computer which devices to check first when starting up. By default, it checks the internal hard drive. If you need to run a diagnostic tool or repair program from a USB drive, you need to change this order so the USB drive comes first.

Navigate to the "Boot" section using arrow keys. You'll see a list of devices — usually "Hard Drive," "USB," "CD/DVD," and others. Use the arrow keys to highlight "USB" or "Removable Media." Then look for an option to move it up in the list — this might be labeled "Boot Priority," and you'll use the + or - keys, or Page Up and Page Down, to reorder. Move USB to the top so it's checked before the hard drive. Then navigate to "Exit" and select "Save and Exit" or "Exit and Save Changes."

Your computer will restart and should now boot from the USB drive if one is plugged in. If it still boots from the hard drive, the USB drive may not be formatted correctly, or the BIOS may not recognize it. Check the manufacturer's instructions for the tool you're trying to run.

Resetting the BIOS if something goes wrong

If you change a setting and your computer won't start, you can reset the BIOS to its factory defaults. Look for an option in the BIOS menu called "Load Defaults," "Reset to Defaults," or "Restore Factory Settings." Select it and confirm. This will undo any changes you made and return the BIOS to how it came from the manufacturer.

If your computer won't even get to the BIOS screen, you can reset it physically. Shut down the computer completely and unplug the power cable. On the motherboard inside the case, there's a small coin-shaped battery called the CMOS battery. If you're comfortable opening your computer, remove this battery for 10 to 15 seconds, then put it back in. This clears the BIOS settings. Plug the power back in and restart — the BIOS will be reset to defaults.

If you're not comfortable opening your computer, contact the manufacturer's support line or take it to a repair shop. A technician can reset the BIOS for you in a few minutes.

When to avoid making BIOS changes

The BIOS controls fundamental hardware settings. A wrong change can make your computer unbootable or unstable. Only open the BIOS if you have a specific reason — you're following instructions from a troubleshooting guide, a technician told you to change something, or you're trying to boot from a USB drive. If you're just curious, it's better to leave it alone.

Never change settings related to processor voltage, memory timing, or security features unless you know exactly what you're doing. These settings can damage hardware or lock you out of your own computer. If a guide tells you to change something in the BIOS and you're not sure what it means, stop and ask for clarification before proceeding.

Frequently Asked Questions

What if I press the BIOS key and nothing happens?

You may have missed the timing window — it's usually only a few seconds. Restart and try again, pressing the key repeatedly as soon as you see the manufacturer's logo. If that doesn't work, try the alternative method: on Windows, use Settings > System > Recovery > Advanced startup. On Mac, hold Command+R during startup.

Can I damage my computer by opening the BIOS?

Opening the BIOS itself won't damage anything. Changing settings can cause problems, but you can always reset to factory defaults. The only real risk is if you physically open the computer to remove the CMOS battery — static electricity can damage components, so ground yourself first by touching a metal part of the case.

Why does my computer keep booting from the USB drive even after I changed the boot order back?

The USB drive may still be plugged in. Many computers check USB devices first even if the hard drive is set as the primary boot device. Unplug the USB drive and restart. If it still boots from USB, go back into the BIOS and make sure the hard drive is actually set to boot first.

Is it safe to change processor or memory settings in the BIOS?

Only if you know what you're doing. Overclocking (running the processor faster) or changing memory timing can make your computer unstable or damage hardware. If a troubleshooting guide tells you to change these settings, follow the instructions exactly. If you're experimenting on your own, you risk breaking something.

What's the difference between BIOS and UEFI?

UEFI is the newer version of BIOS — most computers made after 2010 use UEFI instead. They work the same way from a user's perspective: you restart, press a key, and see a menu. The main difference is that UEFI is faster and supports larger hard drives. You don't need to know which one your computer has — the process for opening it is the same.