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Convert a Disk from GPT to MBR or MBR to GPT Using the chgdtype.tbs Script


This article details using the TBOSDT for BootIt chgdtype.tbs script to automate the conversion between GPT and MBR disk types. This conversion can be especially helpful in cases where a Windows disk type needs to be changed and be able to boot into Windows using the new type.

Conversions from GPT to MBR/EMBR and MBR/EMBR to GPT are supported on both physical disks and virtual disks (.vhd, .vhdx, .vmdk).

Before you begin

  • The chgdtype.tbs script requires TeraByte OS Deployment Tool Suite Pro (TBOSDT) for BootIt, which is included with the purchase of BootIt BM. It can be run from a BootIt BM installation or from BootIt BM boot media. It can also be run from Windows, TBWinRE/PE, or Linux using the applicable version of TBOSDT. Note that you can't convert a disk that contains the currently booted operating system. For example, if you are dual-booting Windows 7 and Windows 8.1 from a single disk you can't convert that disk while booted to either one. However, if you have Windows 7 on one disk and Windows 8.1 on a different disk and they are independent of each other you could boot into either one and convert the other disk.

    If doing the conversion outside of Windows, create the boot media you'll be using (e.g. BootIt BM, TBWinRE, IFL) and include the TBOSDT for BootIt files, if necessary.

    Note: TBOSDT Pro for BootIt is an enhanced version of TBOSDT Pro. Starting with version 1.63, TBOSDT Pro for BootIt is unlocked by entering your BootIt BM key in TBOSDT Pro. For older versions, those who have purchased BootIt BM will have a separate download in their TeraByte account for TBOSDT Pro for BootIt.

  • Create a backup image of the drive being converted. This is highly recommended as conversion requires partitions to be deleted and modified. Alternatively, you may wish to copy the drive to a new disk for the conversion.
  • Be aware of the size of the drive(s) involved. Drives larger than 2TB will normally be limited to 2TB when converted to MBR. Drives larger than 2TB may not be able to be converted depending on how they are partitioned.

  • If converting a Windows 7/8.x/10 drive, check the computer's BIOS and make sure it supports booting the desired type (Legacy BIOS/MBR or UEFI/GPT).

  • Converting an OEM Windows system disk may disable access to the OEM partition and/or recovery partition. If converting to MBR you may need to delete one or more of the additional partitions to get the count to four or less.

  • Converting a GPT disk with more than four partitions (not including the Microsoft reserved partition and EFI System partition, which will both be removed) will result in an EMBR type disk configured with unlimited primary partitions. Depending on the desired outcome, this may require further partition manipulation (e.g. using BootIt BM to load required partitions into the MBR or deleting unnecessary partitions and converting the disk to MBR).

  • For more information on using TBOSDT or running scripts refer to the TBOSDT manuals.


  1. If converting a data-only disk (no Windows installation) skip to Step 2.

    The Windows Recovery Environment (WinRE) is included with Windows 7/8.x/10 and is normally enabled on those systems. The script will attempt to either retain WinRE in a working (enabled) state or in a state which can be easily enabled after the conversion. Alternatively, WinRE can be disabled prior to performing the conversion by booting into Windows on the disk that will be converted, opening an Administrator Command Prompt, and then running the following command:
    reagentc /disable

    To verify that WinRE has been disabled and winre.wim now exists in the C:\Windows\System32\Recovery folder, run the following command (if your Windows partition is not C:, use the letter that's correct for your system):
    dir /a C:\Windows\System32\Recovery

    For a standard installation of Windows you should see winre.wim in the list of files. For OEM installations it may or may not be there, depending on the configuration.

    Note: Due to the nature of WinRE and the multitude of system configurations there may be systems where WinRE requires repairs to function properly after the conversion (regardless of whether or not it was disabled prior to the conversion).

  2. Run TBOSDT for BootIt:

    • In BootIt BM: Click the Scripting icon on the desktop.

    • In Windows (booted and running from a disk other than the one being converted): Run tbosdtw.exe (or tbosdtw64.exe). Alternatively, if TBOSDT for BootIt is installed you can run the chgdtype.tbs script directly and skip Step 3.

    • In TBWinRE/PE (with TBOSDT for BootIt included in the build): Run the the script directly from the Scripts menu (TeraByte - Change Disk Type) and skip Step 3. Otherwise, run the TeraByte OSD Tool menu item.

    • In Linux you will need to start a terminal, go to the directory with the TBOSDT for BootIt files, and then run tbosdt (e.g. "./tbosdt").

  3. Run the chgdtype.tbs script (you may need to change to the scripts folder first or specify the path with the script):
    runtbs chgdtype

    Note: A summary screen will be shown to confirm your selections and the details of the conversion prior to any changes taking place. Before the conversion begins, you can cancel at any time by closing the TBOSDT window.

  4. Select to the type of disk to convert (physical or virtual) and then select the disk.

  5. If converting a GPT disk you will have the choice of creating a System Reserved partition or placing the booting files on the system (Windows) partition. If a System Reserved partition is not required you can reduce the number of partitions needed by not creating one (this can be helpful if the extra partition will result in an EMBR disk when you want an MBR disk). If you are not going to be using BitLocker there is usually no need to have a System Reserved partition.

  6. If a warning/caution is displayed note it before continuing. An example is if the conversion will result in an EMBR type disk.

  7. A summary is displayed detailing what will be done and if a WIndows installation was found.

  8. Press Enter to perform the conversion.

  9. If the converted disk is EMBR (more than four partitions) you will now need to use BootIt BM to load partitions into the MBR or make further partitioning changes to convert to MBR. For Windows disks this must be done before attempting to boot the drive.

  10. For a Windows disk conversion, configure the system to boot the converted disk and boot into Windows. If WinRE was disabled in Step 1, disabled by the script, or disabled previously, open an Administrator Command Prompt and enable it by running the following command:
    reagentc /enable

    If there are issues enabling WinRE, please refer to Repairing the Windows Recovery Environment (WinRE).

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