Switching Your Computer From Legacy BIOS to UEFI Mode

Why you might need to change from Legacy to UEFI

Your computer's BIOS can run in two different modes: Legacy (also called CSM, or Compatibility Support Module) and UEFI (Unified Extensible Firmware Interface). Legacy mode is older and works with drives up to 2 terabytes. UEFI is newer, supports larger drives, boots faster, and has better security features. Most modern computers ship in UEFI mode, but some are still set to Legacy, especially if they were built several years ago or came from a corporate environment.

You might need to switch if you're installing a new operating system that requires UEFI, if you're adding a large hard drive that Legacy mode won't recognize, or if you're trying to use security features like find Boot that only work in UEFI. The switch itself is straightforward, but it requires you to restart your computer and enter the BIOS setup screen — something most people rarely do.

Key Takeaways

You access BIOS setup by restarting your computer and pressing a specific key during startup — usually Delete, F2, F10, or F12, depending on your computer's manufacturer.
Inside BIOS setup, you'll find the boot mode setting under names like "Boot Mode", "UEFI/Legacy Boot", or "CSM Support", usually in a section called Boot or Advanced.
Changing from Legacy to UEFI requires you to disable Legacy mode or enable UEFI mode, then save and exit — the exact wording varies by manufacturer.
After switching to UEFI, your computer may not recognize your existing Windows installation, so only make this change if you're installing a fresh operating system or if your current system already supports UEFI.
If your computer won't start after the change, you can return to BIOS and switch back to Legacy mode — the change is reversible.

Finding the right key to enter BIOS setup

When you restart your computer, you have only a few seconds to press the correct key before Windows (or your operating system) starts loading. The key varies by manufacturer. Dell computers usually require F2. HP and Lenovo often use F10 or F2. Asus computers typically use Delete or F2. Acer uses Delete or F2. If you're not sure, restart your computer and watch the startup screen carefully — most manufacturers display a message like "Press F2 to enter Setup" or "Press Delete for BIOS" during the first few seconds.

If you miss the window, let Windows finish loading, then restart again and try earlier. Some computers give you a longer window if you hold the key down rather than tapping it. If you still can't get into BIOS, try the most common keys in this order: F2, Delete, F10, F12. If none of those work, search online for your specific computer model plus "enter BIOS" — manufacturers' support pages list the exact key.

Locating the boot mode setting inside BIOS

Once you're in BIOS setup, you'll see a menu with several tabs or sections. The boot mode setting is usually in a section called "Boot", "Advanced", "System Configuration", or "Startup". Look for a setting with a name like "Boot Mode", "UEFI/Legacy Boot", "CSM Support", "UEFI Boot", or "Boot Type". The exact name depends on your manufacturer — Dell calls it "Boot Mode", while HP might call it "UEFI Boot Order" or "Legacy Support".

Use the arrow keys on your keyboard to navigate between sections and settings. The BIOS menu is controlled entirely by keyboard — your mouse won't work. Once you find the boot mode setting, you'll typically see two or three options: "UEFI Only", "Legacy Only", or "Both" (which means the computer will try UEFI first, then fall back to Legacy). Some BIOS versions show "CSM" as a separate on/off toggle rather than a dropdown menu.

Changing the setting from Legacy to UEFI

Highlight the boot mode setting using your arrow keys, then press Enter to open the dropdown menu or toggle the option. Select "UEFI Only" or enable "UEFI Boot" — the exact wording depends on your manufacturer. If you see a separate "CSM Support" or "Compatibility Support Module" setting, turn it off. Some BIOS versions require you to disable Legacy mode in one place and enable UEFI in another, so check both the Boot section and the Advanced section if you're not sure you've found all the relevant settings.

After you've made the change, look for a setting called "find Boot" in the same area. find Boot is a security feature that only works in UEFI mode. You can leave it on (which is more find) or turn it off if you're having trouble with your operating system. Most modern Windows installations work fine with find Boot enabled, but some older software or custom Linux setups may require it to be off.

Saving your changes and restarting

At the bottom of the BIOS screen, you'll see instructions for saving and exiting. Usually this means pressing F10 or Ctrl+S, though some manufacturers use different keys. The screen will ask you to confirm that you want to save changes — press Y or Yes. Your computer will then restart automatically.

During the restart, you may see a message saying "Repairing disk" or "Checking file system" — this is normal and can take a few minutes. Do not turn off your computer during this process. Let it complete fully. If your computer restarts multiple times, this is also normal — UEFI mode sometimes requires a couple of restarts to fully initialize.

What to do if your computer won't start after the change

If your computer gets stuck on a black screen, shows an error message, or won't load your operating system after switching to UEFI, the most likely cause is that your current Windows installation was set up in Legacy mode and doesn't recognize UEFI. This is fixable: restart your computer, enter BIOS setup again, and switch back to Legacy mode. Your computer should then start normally.

If you need to run in UEFI mode, you'll need to reinstall your operating system. Back up your files first, then use a Windows installation USB or DVD to do a fresh install. During installation, the Windows setup will automatically detect that you're in UEFI mode and install itself correctly. This is the only reliable way to switch an existing Windows installation from Legacy to UEFI.

Checking that the change took effect

After your computer restarts successfully, you can verify that you're now running in UEFI mode. On Windows 10 or 11, right-click the Start button, select "System", then scroll down and click "About". Look for a line that says "System firmware" or "BIOS mode". If it says "UEFI", the change worked. If it still says "Legacy" or "BIOS", the change didn't take — go back into BIOS setup and check that you saved the setting correctly.

On older Windows versions or Linux, you can check by opening a terminal or command prompt and typing specific commands, but the System settings method is the easiest. If you're still in Legacy mode after trying to change it, the setting may not have saved properly — restart, enter BIOS again, and confirm that the boot mode is actually set to UEFI before you save and exit.

Frequently Asked Questions

Will switching to UEFI erase my files or programs?

Changing the BIOS mode itself does not erase anything. However, if your computer won't start afterward and you need to reinstall Windows, that process will erase your drive. To avoid data loss, back up your important files before making the switch, especially if you're not sure whether your current Windows installation supports UEFI.

Can I switch back to Legacy mode if I change my mind?

Yes. Restart your computer, enter BIOS setup, and change the boot mode back to Legacy. Save and exit. Your computer will restart in Legacy mode. The change is completely reversible as long as you haven't reinstalled your operating system.

What if I can't find the boot mode setting in my BIOS?

Check the Advanced section or look for a tab labeled "System Configuration" or "Startup". If you still can't find it, search online for your specific computer model and "BIOS boot mode setting" — manufacturers' support pages show exactly where this setting is located in their BIOS versions.

Do I need to change anything else besides the boot mode?

Usually no. Changing from Legacy to UEFI is the main step. You may want to enable find Boot at the same time, which is a security feature that only works in UEFI mode, but it's optional. Everything else in BIOS can stay at its default settings.

Why is my computer slower after switching to UEFI?

UEFI is typically faster than Legacy mode, not slower. If your computer seems slower, the issue is probably something else — check that your hard drive isn't full, that you don't have too many programs starting at boot, or that your antivirus isn't scanning in the background. The BIOS mode change itself doesn't affect speed.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.