What changing from Legacy to UEFI means

Legacy BIOS is the older firmware standard that has run computers for decades. UEFI (Unified Extensible Firmware Interface) is the newer standard that replaces it. The difference matters because UEFI supports larger hard drives, boots faster, and offers better security features — but your Windows installation and hard drive must be set up to match whichever mode you choose.

Switching from Legacy to UEFI is not a simple toggle. You cannot just change the setting in BIOS and restart. The process requires backing up your data, wiping your hard drive, and reinstalling Windows in UEFI mode. This is why most people only do it when they are setting up a new computer or replacing their hard drive.

If your computer is working fine in Legacy mode and you have no reason to switch, you do not need to. But if you are building a new system, installing a large drive over 2TB, or your motherboard manufacturer recommends UEFI for your hardware, this guide walks you through the steps.

Key Takeaways

  • Changing to UEFI mode requires a full Windows reinstall — you cannot simply change a BIOS setting and keep your current installation.
  • Back up all your files to an external drive or cloud storage before you start, because your hard drive will be erased.
  • You will need a Windows installation USB or DVD and your Windows product key or Microsoft account credentials.
  • After switching to UEFI, your hard drive partition style changes from MBR to GPT, which is why Legacy and UEFI installations cannot coexist on the same drive.

Check whether your motherboard supports UEFI

Almost all modern motherboards support UEFI, but very old computers (before 2010) may not. The fastest way to check is to restart your computer and enter BIOS setup — usually by pressing Delete, F2, F10, or F12 during startup, depending on your manufacturer. Look for a menu option that says "Boot Mode", "BIOS Mode", or "UEFI Settings".

If you see options for both Legacy and UEFI, your motherboard supports both. If you only see Legacy or BIOS options with no mention of UEFI, your motherboard does not support UEFI and you cannot make this change. Check your motherboard manual or manufacturer website if you are unsure — search for your exact motherboard model plus "UEFI support".

Back up everything on your computer

The conversion process erases your entire hard drive. Before you do anything else, copy all your files to an external USB drive, external hard drive, or cloud storage service like OneDrive, Google Drive, or Dropbox. This includes documents, photos, videos, downloads, and any files in your Desktop or Documents folders.

If you have programs you paid for or installed from sources other than the Microsoft Store, write down their names and where you got them. You will need to reinstall them after Windows is set up again. For programs that came with your computer (like printer software or manufacturer utilities), check the manufacturer website to download fresh copies.

Create a Windows installation USB or DVD

You need a way to install Windows fresh in UEFI mode. Go to Microsoft's website and download the Windows installation tool for your version of Windows (Windows 10 or Windows 11). You will need either a blank USB drive with at least 8GB of space or a blank DVD.

Plug in the USB drive or insert the DVD, then run the Windows installation tool. It will walk you through creating bootable installation media. This takes 10 to 20 minutes. When it finishes, you will have a USB drive or DVD that can start your computer and install Windows from scratch.

Keep this USB drive or DVD in a safe place — you will use it in the next steps.

Change BIOS mode to UEFI and erase your drive

Restart your computer and enter BIOS setup again (usually Delete, F2, F10, or F12 during startup). Look for the Boot Mode, BIOS Mode, or UEFI settings menu. Change the setting from Legacy to UEFI. Some BIOS screens also have a setting called "Secure Boot" — you can leave this on or off; UEFI works either way, though Secure Boot adds extra security.

Look for a setting that says "CSM" (Compatibility Support Module) or "Legacy Support" and turn it off. This ensures your computer boots in pure UEFI mode, not a hybrid mode. Save your changes and exit BIOS (usually by pressing F10 or selecting Save and Exit).

Your computer will restart. Do not let it boot into Windows — instead, plug in your Windows installation USB or insert your DVD immediately. Your computer should boot from the USB or DVD and show the Windows installation screen. If it does not, restart again and look for a boot menu option (often F12 or Esc during startup) to choose the USB or DVD manually.

Install Windows in UEFI mode

The Windows installer will start. Follow the on-screen prompts until you reach the screen that asks where to install Windows. You will see your hard drive listed. Select it and click "Delete" or "Format" — this erases the entire drive and converts it from MBR (Legacy) format to GPT (UEFI) format. Confirm that you want to delete the drive.

After the drive is erased, select it again and click "Next". Windows will install fresh in UEFI mode. This takes 15 to 30 minutes. Your computer will restart several times during installation — this is normal. Do not unplug the USB drive or DVD until Windows finishes and asks you to remove it.

When installation is complete, you will see the Windows setup screen asking for your language, region, and Microsoft account. Sign in with your Microsoft account or local account, and Windows will finish setting up.

Verify UEFI mode is active and reinstall your programs

After Windows finishes setup, restart your computer one more time and enter BIOS again to confirm the Boot Mode is set to UEFI. It should be, but checking takes 30 seconds and confirms the change worked.

Now reinstall the programs you backed up earlier. Download them from their official websites or the Microsoft Store. Restore your files from the external drive or cloud storage you backed them up to. Windows will remember your settings and preferences, but programs need to be installed fresh.

Check that your printer, monitor, and other hardware are working. Windows usually finds drivers automatically, but if a device is not working, visit the manufacturer website and download the latest driver for your hardware model.

Frequently Asked Questions

Can I switch to UEFI without erasing my hard drive?

No. Legacy BIOS uses MBR partition format, and UEFI uses GPT format. They are incompatible, so your drive must be converted. Some third-party tools claim to convert MBR to GPT without erasing data, but they are unreliable and risk data loss. A clean install is the safe approach.

What if my computer will not boot from the USB or DVD?

During startup, look for a boot menu option — usually F12, Esc, or F9. Select it and choose your USB drive or DVD from the list. If that does not work, enter BIOS and check that USB or DVD boot is enabled in the boot order menu. Some computers have USB disabled by default.

Do I need to buy Windows again?

No. Your Windows license stays with your Microsoft account or is tied to your motherboard. When you reinstall Windows, sign in with the same Microsoft account and Windows will recognize your license. If you have a product key, you can enter it during installation instead.

Will my programs and files still work after switching to UEFI?

Yes, as long as they are compatible with your version of Windows. Most programs work the same in UEFI mode as they do in Legacy mode. You will need to reinstall them because your hard drive was erased, but they will function normally once installed.

What if I change my mind and want to go back to Legacy mode?

You can switch back, but it requires the same process: change BIOS to Legacy mode, erase the drive, and reinstall Windows. There is no way to convert a UEFI installation back to Legacy without erasing and reinstalling.