Windows 8 and 8.1 Forums

Convert MBR To GPT To Install Win 8.1

  1. #1

    Posts : 11
    Windows 8.1 Pro

    Convert MBR To GPT To Install Win 8.1

    Ok my daughters Acer laptop already has Windows 8.1 installed. It has a MBR disk. My USB Flash Drive won't boot from it but it does my my desktop so not the USB flash drive.The flash drive was created for UEFI or MBR boot using Rufus. I tried the tutorial in sevenforums to convert the Acer to GPT but it says the boot drive is in use and can't. I tried to boot to a Command Prompt but that gives me an X: drive and I can't change it to C prompt. I have done this before from a boot drive and it worked but won't on this machine. How can I get this converted from MBR to GPT??? How can they make that tutorial work for them? They are doing it from within windows there??? This machine BIOS has nothing for legacy or UEFI or secure boot for sure. Is my only option MBR then? If it is what do I make the flash drive with as Rufus option says for UEFI or MBR but won't boot this machine. Yes I have it to boot first but it lights up but goes straight to windows. Thanks for any insight here.

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  2. #2

    San Jose - California
    Posts : 2,847
    8.1x64PWMC Ubuntu14.04x64 MintMate17x64

    The flash drive was created for UEFI or MBR boot using Rufus
    It will work for both but you have to change the BIOS to appropriate settings ie. MBR to use MBR type or UEFI for UFEI type.
    I tried the tutorial in sevenforums to convert the Acer to GPT but it says the boot drive is in use and can't
    You cannot convert from MBR to GPT while Windows is running. You can only convert when it is offline and in addition you will wipe out the data on the disk.

    I tried to boot to a Command Prompt but that gives me an X: drive and I can't change it to C prompt
    When you boot to a command prompt, you are booting to the Windows Recovery Environment (WinPE), the Drive letter is X: and it is in Ramdisk, it is different from your real drive C:

    FYI, As far as speed goes, it does not make any difference whether you use MBR or GPT. GPT supports large disk capacity > 2TB and more than 4 primary partitions can be created. For Laptop, MBR is fine.

    If you really insist to re-install using GPT, then just change the BIOS to UEFI then boot the Installation USB with UEFI mode. When you get to the screen to install Windows, select Custom Install, on next screen, select each partition an click delete untill you have 1 single unallocated partition then click New, Windows will initialize the disk as GPT & create 4 new partitions, just click next and continue windows installation.

    CAUTION: By doing this, you will wipe out everything on that disk including the Windows 8 OEM Recovery partition, so save anything that you need to save first.
    Last edited by topgundcp; 22 Jul 2014 at 00:25.
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  3. #3

    Posts : 879
    Windows 10

    Quote Originally Posted by uffbros View Post
    The flash drive was created for UEFI or MBR boot using Rufus.

    Why doesn't Rufus create an USB that can be booted in both BIOS and EFI mode?

    If you are using an ISO that can be dual booted in EFI or BIOS mode, you may find that the USB created by Rufus will not preserve the dual EFI+BIOS boot feature.

    Especially, the Windows 8 installation ISOs, that support both EFI and BIOS boot, will be converted to either one or the other mode, depending on the option you selected under Partition scheme and target type: If you select the first option (MBR partition scheme for BIOS or UEFI computer), the USB will be bootable in BIOS-mode only (even on UEFI systems), and if you select any of the other options, the USB will be bootable in EFI mode only (and not bootable on a BIOS system at all).
    Here is more info:
    Windows 7/8 setup: Installing using the MBR or GPT partition style.
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  4. #4

    Posts : 11
    Windows 8.1 Pro

    As stated in my original post.....This laptop BIOS has no UEFI setting. It doesn't have anything about Legacy either. I looked at every window in BIOS. I'll just make a MBR Flash Drive and be done with it. Just wanted to know if it could be done GPT. Thanks.
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  5. #5

    Posts : 879
    Windows 10

    Windows 8 64-bit only support booting from GPT partitions on systems with UEFI firmware.

    Windows and GPT FAQ (Windows Drivers)

    Is UEFI required for a GPT disk?
    No. GPT disks are self-identifying. All the information needed to interpret the partitioning scheme of a GPT disk is completely contained in structures in specified locations on the physical media.

    Can Windows 7, Windows Vista, and Windows Server 2008 read, write, and boot from GPT disks?
    Yes, all versions can use GPT partitioned disks for data. Booting is only supported for 64-bit editions on UEFI-based systems.
      My System SpecsSystem Spec

Convert MBR To GPT To Install Win 8.1
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