Convert MBR To GPT With MBR2GPT In Windows 10 Version 1703

Starting with Windows 10 build 15007, the operating system includes a new console tool, mbr2gpt, which converts an MBR disk (Master Boot Record) to a GPT disk (GUID Partition Table) without modifying or deleting data on the disk. Here is how to use this tool.

MBR or Master Boot Record is the old way of partitioning disks where a special boot sector at the beginning of the partitioned storage was used to identify where the bootable operating system was located. MBR was used when PCs had a BIOS. With the newer UEFI standard replacing BIOS, GPT (GUID Partition Table) was introduced. It defines a standard layout for partition tables using GUIDs (globally unique identifiers).

Before Windows 10 Creators Update, you needed to decide at the time of formatting the disk whether to use MBR or GPT, meaning the data on the disk had to be erased to change the partition table style. MBR2GPT introduced in Creators Update lets you convert an existing MBR disk to a GPT disk without erasing it.

MBR2GPT.exe is designed to be run from a Windows Preinstallation Environment (Windows PE) command prompt, but it can also be run from a regular installed copy of Windows 10. It is a console tool, which doesn't have any graphical user interface. It should be started with a special set of arguments.

The syntax of the command is as follows:

MBR2GPT /validate|convert [/disk:] [/logs:] [/map:=] [/allowFullOS]

Here is a brief description of the available command line parameters.

/validate Instructs MBR2GPT.exe to perform only the disk validation steps and report whether the disk is eligible for conversion.

/convert Instructs MBR2GPT.exe to perform the disk validation and to proceed with the conversion if all validation tests pass.

/disk: Specifies the disk number of the disk to be converted to GPT. If not specified, the system disk is used. The mechanism used is the same as that used by the diskpart.exe tool SELECT DISK SYSTEM command.

/logs: Specifies the directory where MBR2GPT.exe logs should be written. If not specified, %windir% is used. If specified, the directory must already exist, it will not be automatically created or overwritten.

/map:= Specifies additional partition type mappings between MBR and GPT. The MBR partition number is specified in decimal notation, not hexidecimal. The GPT GUID can contain brackets, for example: /map:42={af9b60a0-1431-4f62-bc68-3311714a69ad}. Multiple /map options can be specified if multiple mappings are required.

/allowFullOS By default, MBR2GPT.exe is blocked unless it is run from Windows PE. This option overrides this block and enables disk conversion while running in the full Windows environment.

Currently, the tool supports conversion of disks with installed Windows 10 version 1507, 1511, 1607 and 1703. It does not officially support Windows 7 or Windows 8, even in offline mode. Microsoft recommends you to upgrade to Windows 10 if you want to try the tool in action.

The following video describes the utility:

11 thoughts on “Convert MBR To GPT With MBR2GPT In Windows 10 Version 1703

  1. EBIN

    So does this also work on non-system partitions? ie. ones only with data on it

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    1. Sergey Tkachenko Post author

      I haven’t tried. I think it should work.

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  2. Patrick Pasqualino Di Simone

    i get a error saying can only run from a pe environment

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    1. jupe

      even when yousing the following switch ?

      /allowFullOS

      By default, MBR2GPT.exe is blocked unless it is run from Windows PE. This option overrides this block and enables disk conversion while running in the full Windows environment.

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  3. Jasonjay

    “Microsoft recommends you to upgrade to Windows 10 if you want to try the tool in action.”

    Of course they do. Couldn’t have older versions of Windows that are still under support and still receiving updates having any of these new features as wekk. That’s too much effort from the biggest fucking software company in the world.

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  4. murat

    it did the trick with “/allowFullOS” command.

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  5. Bill Woodruff

    What possible benefit(s) could result from the conversion ?

    thanks, Bill

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    1. Sergey Tkachenko Post author

      GPT is a modern standard which resolves a lot of MBR limitations. MBR only works with disks up to 2 TB in size. MBR also only supports up to four primary partitions. GPT-based drives can be much larger, with size limits dependent on the operating system and its file systems. GPT also allows for a nearly unlimited number of partitions. You create up to 128 primary partitions without having an extended partition.

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  6. Boris Winebrand

    Microsoft Windows [Version 10.0.15063]
    (c) 2017 Microsoft Corporation. All rights reserved.

    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
    Cannot find OS partition(s) for disk 0

    please help

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    1. Boris Winebrand

      found the solution – restored the 500mb recovery partition and the problem solved

      thank you!

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  7. Boris Winebrand

    ok, found the solution:

    Create A New Recovery Partition

    Note: here we take Windows 8 for example.
    Step 1: Download your Windows ISO directly from Microsoft, which will require your product key to install. (Note: In many cases, this is included with your Windows computer.)
    Step 2: Use Microsoft’s tool to create installation media for Windows.
    Step 3: Look for the Sources folder, where you’ll find install.esd. This is the recovery partition, basically, but in its current state it is useless. To make it work for you, you have to first move it from the ISO or DVD to a location on your hard disk. Next, you need to convert it from install.esd to install.wim via some converters like WimConverter tool, and then copy the install.wim file to a new folder on your C:\ drive, labeled C:\Win81-Recovery. The next stage is to register the file so that Windows knows it is there and can create a recovery drive.
    Step 4: Right-click the Windows Start screen button and select Command Prompt (Admin) on the desktop. Next, in the command line, enter:
    REAGENTC /SetOSImage /Path C:\Win81-Recovery\INSTALL.WIM /Index 1
    Tip: This will register the INSTALL.WIM file as your PC’s recovery image.

    Step 5: Type: REAGENTC /Info.
    Step 6: Type: exit.

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