source: Convert an existing Windows 10 Installation from Legacy BIOS to UEFI
Convert MBR to GPT without data loss
Windows has an in-built tool, called MBR2GPT which can help to convert a Legacy Windows 10 Installation(also called MBR), to modern UEFI, based on a GPT partition scheme. There are multiple steps involved in the process and some pre-requisites, discussed below:
Pre-requisites:
- The MBR disk must have at most 3-partitions.
- The OS must be 64-bit.
- Bitlocker or encryption must be turned off.
- There should be an Operating system on the disk.
- One of the partitions must be active(confirm that from disk Management).
- No dual boot.
- Windows 10 version must be at least version 1703.
How MBR2GPT works.
Step 1: Boot to the Recovery environment
- On the Lock screen, press and hold the Shift key while choosing Restart from the Power menu. Continue pressing the shift key until you see the Windows Recovery environment, asking you to select an option.
- Click Troubleshoot>Advanced options>Command Prompt.
- The computer would restart.
- Login to your account.
Step 2: Validate if the MBR2GPT tool can convert your disk
On the Command Prompt Window, our next step would be to check if the tool can convert the disk to GPT. To do this, execute the following command:mbr2gpt.exe /validate
The output should tell you if the validation is successful. If the disk is validated, conversion is possible.
Step 3: Convert the disk.
The next step is to convert the disk. For that, use the /convert switch.
mbr2gpt.exe /convert
The process would take some minutes and tell you the output.
Step 4: Change the boot order in firmware Settings
Now to boot from GPT, the settings in the firmware need to be changed. Boot to the PC’s firmware settings, and do the following:
- Boot method: UEFI from Legacy.
- UEFI-CSM: Disabled.
- Secure Boot: ON.
The boot order would usually show Windows Boot Manager at the top. Save the changes in the BIOS menu.
The device should now have a UEFI boot method with a GPT disk layout.