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Currently I have Ubuntu 20.04 installed in UEFI mode and Windows installed in Legacy. I would like to convert Windows to UEFI to have dual boot.

My disk currently

It is installed in MBR mode and here is the partition table

Possible solutions

I found out how to convert my disk to GPT under Ubuntu with sudo gdisk /dev/sda, but I think that Windows will no longer be recognized by UEFI.

I also found out how to do it from Windows, with mbr2gpt.exe /convert /disk:0 /allowfullOS, but I'm afraid that Windows doesn't know what to do with ext4 partitions, and that it overwrites the current EFI partition.

What should I do ?

PS: Sorry for my English

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  • Might be easier to start over & install Windows, then Ubuntu, both in UEFI boot mode & restore your data from backups. I think I saw someone that tried the Windows conversion & it failed & they had to reinstall anyway. Windows wants additional partitions with UEFI/gpt. docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/… At minium, reinstall of boot loaders(grub & Windows) as UUIDs change, perhaps chkdsk for NTFS & fsck for ext4 partitions as repairs.
    – oldfred
    Commented Jan 5, 2021 at 21:01
  • according to this website it's pretty easy to convert windows to uefi, and ubuntu is already in uefi, so I hope to be able to do the conversion easily. But if nobody has a safe solution I'll make a backup of ubuntu and use mbr2gpt.exe (because windows is really too long to install).
    – Rayzeq
    Commented Jan 5, 2021 at 21:24
  • or maybe I'll just keep switching OSes by changing the bios mode.
    – Rayzeq
    Commented Jan 5, 2021 at 21:27
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    This user had two drives so each could be different. But was not able to make it work. ubuntuforums.org/showthread.php?t=2408541 & docs.microsoft.com/en-us/windows/deployment/mbr-to-gpt
    – oldfred
    Commented Jan 5, 2021 at 22:01
  • By reading the second link in your message, I saw that it didn't work with extended partitions, so I think I'll just reinstall Windows.
    – Rayzeq
    Commented Jan 5, 2021 at 22:40

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