If you have started a Windows 11 upgrade in your corporate environment, you may have heard about MBR2GPT. MBR2GPT.exe is a tool that helps convert the disk partition style on Windows PC from the legacy Master Boot Record (MBR) to GUID Partition Table (GPT) without changing or deleting data on the hard drive.
This article will teach you about the MBR2GPT tool for Windows 10 and 11 and how you can use it yourself.
Part 1. What Is MBR2GPT Tool on Windows 10/11?
MBR2GPT.EXE converts a disc from the Master Boot Record (MBR) partition style to the GUID Partition Table (GPT) partition style. It is designed to be run from a WinPE (Windows Preinstallation Environment) Command Prompt. However, with the /allowFullOS option, the program can also be launched from the entire Windows 10 operating system (OS).
The MBR2GPT tool can be found in the directory Windows\System32 on PCs running Windows 10 version 1703 or later and Windows 11.
Both Windows PE and the complete OS environment have this utility available. You must first upgrade the Windows PE image (winpe.wim, boot.wim) with the Windows ADK 1703, or a later version, in order to utilize this tool in a deployment task sequence using Configuration Manager or Microsoft Deployment Toolkit (MDT).
You may also be interested in: How to Fix MBR2GPT Validation Failed?
Part 2. How To Use the MBR2GPT Tool?
Before running the command, you first need to identify the correct disk number. Here’s how:
- 1. Open Command Prompt as an Administrator.
- 2. Type
diskpartand press Enter. - 3. Type
list diskand press Enter. You will see a list of disks connected to your system. Identify the disk number for your Windows installation (e.g., Disk 0).
Now, you can run the conversion command. We will cover two scenarios:
Scenario 1. Converting Within Full Windows OS Environment
This is the most common method. Use the /allowFullOS parameter. Replace 0 with your actual disk number.
mbr2gpt /convert /disk:0 /allowfullos
Scenario 2: Converting within Windows PE
If you are in the Windows Preinstallation Environment, the command is slightly different:
mbr2gpt /convert /disk:0
Part 3. Understanding MBR2GPT Commands (e.g., /allowfullos)
The MBR2GPT tool has several parameters. The most important one is /allowfullos. Here's what it does and when you should use it:
Command |
Description |
mbr2gpt /validate |
Validates disk eligibility for conversion. |
mbr2gpt /convert |
Performs the conversion from MBR to GPT. |
/disk: |
Dual-boot users |
/allowfullos |
Allows the tool to run within the full Windows OS. |
- What is
/allowfullos? This parameter allows the MBR2GPT tool to run from within the full Windows operating system (like your normal desktop) instead of requiring you to boot into the Windows Preinstallation Environment (WinPE). - When to use it? If you are getting an error like "MBR2GPT cannot run in full OS", adding this parameter is the solution. It is the standard way to perform the conversion for most users.
- Example Command:
mbr2gpt /convert /disk:0 /allowfullos
Part 4. The Limitations of MBR2GPT
Though MBR2GPT looks like a day-savior tool, it does come with some limitations.
- Firmware vs. Partition Limitation: MBR2GPT is not at all the same as BIOS to UEFI conversion It converts partition layout, while the latter changes the system's firmware from Legacy BIOS to UEFI.
- Specific Execution Timing: The tool must be run before the BIOS-to-UEFI conversion during an upgrade, preferably within the Windows PE environment. Running it after the firmware conversion often leads to failure.
- Lack of Official Support: GPT or Legacy layouts are not officially supported; therefore, you may lack technical recourse if an error occurs during or after the conversion process.
- Irreversibility of Conversion: You cannot undo the steps once the disk has been converted. Also, in case you have performed the layout during an upgrade, you cannot revert to a previous version of windows. This limitation is standard, irrespective of the brand of computer you are using.
- Partition Count Restriction: To function at full capacity, the target disk must contain fewer than four partitions. Certain hardware, such as Dell models, may create extra recovery partitions during upgrades that can trigger a conversion failure.
- Driver Package Accuracy: You must provide the exact driver package for your specific hardware model if using the tool in a sequence designed for multiple models. The setup will disregard incorrect variables, making driver precision a critical factor.
Part 5. Troubleshooting When Using MBR2GPT
The tool can return various common errors. But don't worry, as you can resolve them in most cases. Here is the list of return codes you may get when using the MBR2GPT utility:
Return code |
Description |
| 0 | The conversion was completed successfully. |
| 1 | The conversion was canceled by the user. |
| 2 | The conversion failed due to an internal error. |
| 3 | The conversion failed due to an initialization error. |
| 4 | The conversion failed due to invalid command-line parameters. |
| 5 | The conversion failed due to an error in reading the geometry and layout of the selected disk. |
| 6 | The conversion failed because one or more volumes on the disk are encrypted. |
| 7 | The conversion failed because the geometry and layout of the selected disk didn't meet the requirements. |
| 8 | The conversion failed due to an error while creating the EFI system partition. |
| 9 | The conversion failed due to an error installing boot files. |
| 10 | The conversion failed due to an error while applying the GPT layout. |
| 100 | The conversion to the GPT layout succeeded, but some boot configuration data entries couldn't be restored. |
Fix #1: MBR2GPT Disk Layout Validation Failed
This is one of the most common errors we find during the MBR to GPT conversion. It may be due to the wrong syntax or system you are using. MBR2GPT.exe only applies to Windows 10 version 1703 or later. The error can also occur if your system does not support the BIOS you are converting.
To solve this, check the following:
- That your syntax is correct
- Your system supports UEFI BIOS
- Check the type of BIOS you are currently using
- Check if your system is not Windows 7,8, 8.1, or earlier versions of Windows 10. It should be Windows 10 version 1703 or later, or Windows 11 if you want to use MBR2GPT
You can also refer to this video for a complete guide to fix the MBR2GPT disk layout validation failed error.
Fix #2: MBR2GPT Cannot Find OS Partition
There could be many technical reasons behind this error. The most common one is that your system has bad entries in the boot configuration. Check the video below to solve this problem quickly.
Here is also a step-by-step guide for you to fix “MBR2GPT can’t find OS partition”:
Step 1. Open the diskpart and check for any bad entries. Use the syntax as follows:
▸diskpart
▸select disk 0: the operating system disk
▸list partition
▸select partition 2: because here partition 2 is the partition where the Windows OS is installed
▸assign drive letter= w (for example)
▸select partition 1: because here partition 1 is the system-reserved partition
▸assign drive letter= b (for example)
After this, you can easily take a step ahead of the system boot partition files to examine the Windows system partition further and determine whether the boot folder is present.
Step 2. Use the command X: Sources>dir /a w: Run the command X: Sources>dir /a b: to verify the system-reserved partition if the necessary boot folders are not present.
Step 3. After locating the boot folder in the system partition or system reserved partition, you must use the command X: Sources>dir /a b: Boot to launch the bcdedit program and direct it to the location of the boot configuration data store you just located.
Step 4. Identify any invalid entries at this point. Type X: Sources>bcdedit /store B:bootbcd /enum all to run the command. There are numerous cues for incorrect or subpar entries. For instance, unknown might be found in a few entries. They might be left over from an earlier Windows installation or brought on by malicious software.
Step 5. Copy the bad entry's identification. Next, navigate to the store once more with bcdedit and instruct it to remove the error-prone entry using the copied identifier. Finally, take The Bad Entry Out.
Step 6. To see if everything is working correctly now, try running the command X: Sources>bcdedit /store B:bootbcd /enum all once more. If everything goes as planned, use the MBR2GPT utility once more. This time, you can finish it successfully.
Check out this video to learn more about the process in a visual format.
Fix #3: MBR2GPT Is Not Recognized
The leading cause of this version is your Windows version. You will get this error if you run any version other than windows 10 or 11.
To fix this error, you may simply upgrade your windows to version 10, and this error will not occur again. You can check your Windows version using the System Information dialogue box.
Fix #4: MBR2GPT Cannot Find Room for the EFI System Partition
This error comes up when you don't have enough free space on your computer's system or C allocated drive. In some cases, this error can also occur if there is no unallocated disk space on your system.
You can remove this error by shrinking the C drive to form a new unallocated space. Then, you can move the unallocated space to the front partition of the disk. You can also use any third-party tool to perform this step. Make sure to back up data before proceeding.
Summing up
We hope this article was an eye-opener for you. Remember that facing errors during MBR2GPT tool conversion is a typical process. You will get a chance to learn the intricacies of the computer system while using this tool. Good luck.
For Windows XP/Vista/7/8/10/11
For macOS X 10.10 or later
1. What is the MBR2GPT tool and why is it used?
MBR2GPT.exe is a Microsoft command-line utility used to convert a disk’s partition style from Master Boot Record (MBR) to GUID Partition Table (GPT) without modifying or deleting the data on the disk. It is primarily used by users who want to switch from Legacy BIOS to UEFI firmware. This conversion is essential for enabling modern security features like Secure Boot and is a prerequisite for upgrading to Windows 11, which requires a GPT partition style.
2. Can I use MBR2GPT to convert a disk without losing data?
Yes, MBR2GPT is specifically designed to perform a non-destructive conversion. Unlike traditional methods that require wiping the drive and reinstalling Windows, MBR2GPT adds GPT components to the existing MBR partition structure. However, as with any system-level disk operation, it is a "best practice" to back up your data before proceeding to account for potential power failures or hardware-specific errors during the process.
3. What are the system requirements for running MBR2GPT?
To successfully run the MBR2GPT tool, your system must meet these specific criteria:
1. OS Version: Windows 10 or later.
2. Disk Type: The tool only converts system disks (the disk containing the OS). It cannot be used on non-system data disks.
3. Partition Limit: The MBR disk must have at most three primary partitions.
4. Firmware Support: The motherboard must support UEFI mode.
5. Encryption: If the disk is encrypted with BitLocker, protection must be suspended before starting the conversion.
4. How do I use MBR2GPT to convert MBR to GPT?
The conversion process involves two main steps: validation and conversion.
1. Open Command Prompt as Administrator and type the following to verify the disk is eligible: mbr2gpt /validate /allowFullOS
2. If the validation returns "successful," run the conversion command: mbr2gpt /convert /allowFullOS
Once finished, you must restart your computer and enter your BIOS/UEFI settings to change the boot mode from Legacy to UEFI.
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