Tutorial: Convert Windows 10 From Legacy to UEFI without Data Loss

• Overview of Legacy BIOS and UEFI
• Why need to convert Windows 10 from Legacy BIOS to UEFI?
• How to convert Windows 10 from Legacy BIOS to UEFI without data loss?
• Summary

Overview of Legacy BIOS and UEFI

Before trying to convert Windows 10 from Legacy BIOS to UEFI, it's better to first learn some basics about these two boot modes.

On the whole, the Legacy BIOS and UEFI are two different boot methods, and the main difference lies in the process the firmware uses to find the boot target. The firmware is software that acts as an interface between the hardware (motherboard) and the OS.

♦ Legacy BIOS

Legacy BIOS is the boot process used by BIOS firmware, which stores a list of bootable devices installed on your PC on a priority order. When the computer is powered on, the BIOS performs Power On Self-Test (POST). Once done, the firmware will load the first sector of each storage target into memory and scan it for a valid MBR.

If it is found, the firmware will pass execution to the boot loader code in MBR that enables users to select a partition to boot from. If no valid MBR is found on the current device, it will proceed to the next one in the boot order. But, if no valid MBR is found on all installed bootable devices, Windows cannot boot. In this case, you might meet an "Invalid Partition Table" error on your devices.

♦ UEFI Boot 

UEFI Boot is the abbreviation of Unified Extensible Firmware Interface. It is considered the successor to the Legacy BIOS. The firmware in UEFI boot keeps a list of valid boot volumes called EFI service partitions.

During the POST procedure, the UEFI firmware will scan all the bootable storage devices on your machine for a valid GPT and find an EFI service partition to boot from. If it does not find any EFI boot partition, the firmware will be back on the Legacy BIOS boot method. If both methods don’t work, Windows will fail to boot up.

Why need to convert Windows 10 from Legacy BIOS to UEFI?

From above, you should know what are Legacy BIOS and UEFI boot methods and how they work during Windows startup. So, why do some users want to convert Windows 11, 10, 8, and 7 from Legacy BIOS boot mode to UEFI boot mode? This might be because UEFI has the following advantages over BIOS:

● The UEFI allows users to handle a hard drive that is over 2TB while the old Legacy BIOS cannot since the UEFI uses a GPT disk, but Legacy BIOS uses the MBR disk.

● UEFI can support up to 128 primary partitions on a GPT disk while BIOS can have a max of 4 primary partitions on an MBR disk.

● The UEFI firmware can ensure a faster booting process than the BIOS due to various optimization and enhancements.

● UEFI supports Secure Boot, which can help prevent boot-time viruses from loading.

How to convert Windows 10 from Legacy BIOS to UEFI without data loss?

Prior to converting Legacy BIOS to the UEFI boot method, you should ensure your motherboard supports EFI/UEFI. Then convert the disk with Windows 10 installed from MBR to GPT since the UEFI uses the GUID Partition Table (GPT) and the Legacy BIOS uses the MBR partition table. At last, change the boot mode from Legacy BIOS to UEFI in BIOS settings. Specific steps are listed below:

★Tip:

Only Windows 11, 64-bit of Windows 10, Windows 8, or Windows 7 can boot from the GPT disk and use the UEFI boot mode. So, please first verify your computer's motherboard supports UEFI or EFI boot and that the system is 64-bit, if not, please upgrade it.

Step 1. Convert MBR boot disk to GPT without data loss

To convert the system disk from MBR to GPT, you can enter the WinRE environment and use the Windows inbuilt DiskPart command line. However, that will delete all partitions and data, of course, the OS included. So you have to reinstall OS from scratch after conversion. To convert it without data loss and then change BIOS to UEFI without reinstalling the operating system, you can turn to AOMEI Partition Assistant Professional.

This software can convert disk (either system disk or data disk) between MBR and GPT without deleting any existing partitions. You can click on the above button to download the demo version and follow the steps to complete the task.

1. Install and launch AOMEI Partition Assistant Professional. Right-click the system disk and choose “Convert to GPT”.

2. Click “OK” to confirm your operation.

3. Click on “Apply” to commit the pending operation.

Then the computer will finish the operation in Win PreOS mode.

Step 2. Convert Windows 10 from Legacy BIOS to UEFI

After you have converted the Windows 10 system disk from MBR to GPT, now need to reboot the system, boot into BIOS and select UEFI firmware.

PS.: If you don’t switch your firmware from BIOS to UEFI after converting, you cannot boot into the operating system.

1. Power on your computer, and continuously press a specific key when it starts up to enter the BIOS Setup menu.

2. When prompted in the BIOS screen, press F2 to access the BIOS Setup Utility. After a few moments, the BIOS Setup Utility appears.

3. In the BIOS Setup Utility, navigate to the “Boot” tab on the top menu bar.

4. The Boot menu screen appears. Select the UEFI/BIOS Boot Mode field and use the "+/-" keys to change the setting to UEFI.

5. Press the "F10" key to save changes and exit BIOS.

Summary

So, to convert Windows 10 from Legacy BIOS to UEFI without data loss or reinstalling operating system, the AOMEI Partition Assistant Professional can help you a lot. Besides that, it can also help you to transfer OS from MBR to GPT disk, extend NTFS system drive without rebooting computer, repair damaged MBR, etc. To manage disk partition in Windows Server OS, you can use the AOMEI Partition Assistant Server.