Convert Windows 10 from Legacy BIOS to UEFI without Data Loss  

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  1. ntd252
    Posts : 88
    Windows 10 21H2
       New #90

    Brink said:
    Hello ntd252,

    I wouldn't recommend doing this when you have a multiboot system like that. It will most likely break it.
    Is there any way to do it quicly?
    In the past, I installed Windows 7 first with a 100MB System Reserved, then Windows 10 and last Linux Mint.
    Linux uses Grub2, while Windows7/10 use Windows boot manager.
    I will be sad if I have to copy everything from current disk, convert it and then get data back.
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  3. Brink
    Posts : 68,881
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       New #91

    Not that I'm aware of.

    You might create a separate thread in the Installation & Upgrade forum area to see if someone may know an easier way.
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  4. bayustev
    Posts : 70
    Windows10 pro x64,Version 1803
       New #92

    halo, can i reverse from uefi boot to legacy ? thanks
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  5. Brink
    Posts : 68,881
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       New #93

    Currently, that requires a clean install.
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  7. NavyLCDR
    Posts : 18,432
    Windows 11 Pro
       New #94

    bayustev said:
    halo, can i reverse from uefi boot to legacy ? thanks

    Brink said:
    Currently, that requires a clean install.
    I must disagree, @Brink. The user can create a backup image of the Windows partition. Then they can manually setup the HDD/SDD with MBR format partitioning for legacy BIOS booting using a couple of different methods - manually with diskpart commands or a boot drive containing partitioning software such as Kyhi's recovery drive. Restore the Windows partition from the backup image and recreate the legacy BIOS boot files using the bcdboot command.
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  8. Brink
    Posts : 68,881
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       New #95

    That's good to hear, but not something for the average bear.
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  9. cereberus
    Posts : 15,480
    Windows10
       New #96

    Brink said:
    That's good to hear, but not something for the average bear.
    I would say the average bear could do it, but a newbie would struggle.

    I will prepare a guide which could be whipped up into a tutorial.

    I have the basics in the guide I wrote to update small storage tablets.
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  10. slamdunk
    Posts : 2
    Windows 10
       New #97

    When I run
    mbr2gpt /convert /allowfullOS this happens:

    Code:
    MBR2GPT will now attempt to convert the default book disk.
If conversion is successful the disk can only be booted in GPT mode.
These changes cannot be undone!

MBR2GPT: Attempting to convert disk 0
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Disk layout validation failed for disk 0
MBR2GPT: Conversion failed
    Any idea on how to fix this
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  11. Brink
    Posts : 68,881
    64-bit Windows 11 Pro for Workstations
    Thread Starter
       New #98

    Hello slamdunk, and welcome to Ten Forums.

    What does it report when running the command below?

    mbr2gpt /validate
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  13. slamdunk
    Posts : 2
    Windows 10
       New #99

    Brink said:
    Hello slamdunk, and welcome to Ten Forums.

    What does it report when running the command below?

    mbr2gpt /validate
    Thanks.
    I get this

    Code:
    C:\WINDOWS\system32>mbr2gpt /validate
ERROR: MBR2GPT can only be used from the Windows Preinstallation Environment. Use /allowFullOS to override.

C:\WINDOWS\system32>mbr2gpt /validate /allowFullOS
MBR2GPT: Attempting to validate disk 0
MBR2GPT: Retrieving layout of disk
MBR2GPT: Validating layout, disk sector size is: 512 bytes
Disk layout validation failed for disk 0
    EDIT: Never mind. I had 4 partitions then I deleted an unused one now it works.
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