Converting a hard drive from GPT to MBR.

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  1. Bat Boy 42
    Posts : 4
    Windows 10
       New #1

    Converting a hard drive from GPT to MBR.


    I want to convert my GPT hard drive to mbr.

    I'm using a bootable USB ISO.

    Just one OS (Windows 10 - 20H2).

    I have followed these instructions and they seem to have worked (when I reopen the command prompt the mark under gpt disappears).

    Problem is once Windows install and I look using the command prompt it shows the hard drive as gpt once again.

    Is it possible that the conversion to mbr does happens but once Windows starts installing it switches back to gpt by default?
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  3. Berton
    Posts : 12,415
    Win10 Version 21H2 Pro and Home, Win11 Pro
       New #2

    There doesn't seem to be much basic performance difference between MBR and GPT but GPT is necessary with drives larger than 2TB. But the support for GPT must be available in the BIOS and Enabled. An Operating System reads the BIOS to know what resources are available.
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  4. Bat Boy 42
    Posts : 4
    Windows 10
    Thread Starter
       New #3

    My drive is a 1TB SSD if it makes any difference.
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  6. Ghot
    Posts : 17,612
    Win 10 Home 10.0.19044.1706 (x64) [21H2]
       New #4

    Bat Boy 42 said:
    My drive is a 1TB SSD if it makes any difference.


    If you don't set the BIOS to Legacy (MBR), the Windows installer will partition the drive as GPT.


    Is there some reason you want it to be MBR?
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  7. Bat Boy 42
    Posts : 4
    Windows 10
    Thread Starter
       New #5

    Ghot said:
    If you don't set the BIOS to Legacy (MBR), the Windows installer will partition the drive as GPT.
    Thank you. How would I go about doing that? I took a look in my BIOS and I couldn't see anything referring to MBR. Mine is a Lenovo Yoga C930.
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  8. Ghot
    Posts : 17,612
    Win 10 Home 10.0.19044.1706 (x64) [21H2]
       New #6

    Bat Boy 42 said:
    Thank you. How would I go about doing that? I took a look in my BIOS and I couldn't see anything referring to MBR. Mine is a Lenovo Yoga C930.


    I wouldn't choose MBR if I were you unless it's seriously necessary.
    Most all of the guides and tutorials for Windows 10 assume a GPT partition.

    Is there some particular reason you want it to be MBR?




    Converting a hard drive from GPT to MBR.-image2.png
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  9. Matthew Wai
    Posts : 7,451
    Windows 10 Home 20H2
       New #7

    Bat Boy 42 said:
    I want to convert my GPT hard drive to mbr.
    Have you run the following DiskPart command?

    Convert MBR

    Bat Boy 42 said:
    Thank you. How would I go about doing that? I took a look in my BIOS and I couldn't see anything referring to MBR. Mine is a Lenovo Yoga C930.
    On my boot menu below, "PNY OU3 3.0 PMAP" refers to booting in Legacy mode, applicable to an MBR disk, while "UEFI: PNY OU3 3.0 PMAP" refers to booting in UEFI mode, applicable to a GPT disk. If I had an MBR disk, I would have to select "PNY OU3 3.0 PMAP".


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  10. Bat Boy 42
    Posts : 4
    Windows 10
    Thread Starter
       New #8

    Trying to upload some photos but nothing happens (must be my lucky day).

    This is what I get from my BIOS:









    - - - Updated - - -

    Matthew Wai said:
    Have you run the following DiskPart command?

    Convert MBR
    I have, it says it has been successfully converted and then I proceed to install Windows, but when I re-enter the command prompt once Windows has installed it shows the hard drive as gpt again.
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  11. Megahertz
    Posts : 3,957
    Windows 7 HP 64 - Windows 10 Pro - Lubuntu
       New #9

    Bat Boy 42 said:
    I want to convert my GPT hard drive to mbr.

    I'm using a bootable USB ISO.
    Just one OS (Windows 10 - 20H2).
    I have followed these instructions and they seem to have worked (when I reopen the command prompt the mark under gpt disappears).

    Problem is once Windows install and I look using the command prompt it shows the hard drive as gpt once again.

    Is it possible that the conversion to mbr does happens but once Windows starts installing it switches back to gpt by default?
    Managing disk partitions is a risky task. Make sure you have all your data backed up.

    What do you want to do:
    - Convert a data drive from GPT to MBR?
    - Convert a boot able drive from GPT to MBR?
    - Do a clean install using a win 10 installation drive and convert the drive from GPT to MBR?

    If it is a data drive you can convert from GPT to MBR.
    Diskpart commands will clean up the drive. To convert without loosing data you must use a program like Mini Toll partition wizard .

    But if the drive is a boot able drive, you can't just convert from UEFI - GPT to Legacy - MBR. You have to make sure your BIOS can use Legacy boot drive.
    You have to boot from an external drive (like WinPE), launch Mini Toll partition wizard, convert from GPT to MBR and rebuild bcdboot.

    diskpart
    list volume (take note of windows partition letter)
    select volume x (replace x with the windows partition letter)
    active
    exit
    bcdboot C:\Windows /s C: /f BIOS
    exit
    Last edited by Megahertz; 27 Apr 2021 at 13:34.
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  12. Matthew Wai
    Posts : 7,451
    Windows 10 Home 20H2
       New #10

    Bat Boy 42 said:
    when I re-enter the command prompt once Windows has installed it shows the hard drive as gpt again.
    Do you mean there is an asterisk in the "Gpt" column as shown below?

    Code:
    DISKPART> List Disk

  Disk ###  Status         Size     Free     Dyn  Gpt
  --------  -------------  -------  -------  ---  ---
  Disk 0    Online          465 GB      0 B        *
  Disk 1    Online           60 GB      0 B
  Disk 2    Online         7388 MB      0 B
  Disk 3    No Media           0 B      0 B
  Disk 4    Online           28 GB      0 B
    Bat Boy 42 said:
    I'm using a bootable USB ISO.
    Can you post a photo of the boot menu showing the bootable USB device you have used to clean install Windows 10?
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