Legacy Boot Preparation for Windows 11

By | October 7, 2025
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Before upgrading a PC that does not have secure boot running and TMP enabled, you need to prepare it in person with the following BIOS changes:

1) In Disk Management, verify the disk number (x), then run this CMD:

mbr2gpt /convert /disk:X /allowFullOS

Warning: This will make the PC unbootable until UEFI is enabled!

2) Reboot into the BIOS and change the following (apply as you go):

  • General > Boot Sequence > Boot List Option > Select: UEFI
  • General > Advanced Boot Options > Deselect: Enable Legacy Option ROMs
  • Secure Boot > Select: Enable
  • Security > TMP > Select Enable

Windows should now boot up normally, and you can install Windows 11 in the future.

Initiate the upgrade: https://www.microsoft.com/en-us/software-download/windows11

Troubleshooting:

Disk conversion fails:

  1. Move Boot Files from “Recovery Partition”   to “OS” using this CMD: Bcdboot c:\Windows /s C:
  2. Diskpart
  3. Select disk 0
  4. Select partition 3
  5. Active
  6. Select partition 2
  7. Delete partition
  8. To Delete the OEM Partition
  9. Select partition 1
  10. Delete partition overrideMbr2gpt.exe /convert /disk:0 /allowfullos

Boot Fails

1) Boot from Win 10 Install media > Troubleshoot > CMD

bootrec /fixmbr

bootrec /fixboot

bootrec /scanos

bootrec /rebuildbcd

bootsect /nt60 sys

2) Run startup repair