By Emily / Last Updated September 22, 2021

MBR2GPT Cannot find OS Partition for Disk 0?

Hi, experts, when i trying to convert my Win10 boot disk from MBR to GPT partition table,  it keeps failing with the "Cannot find OS Partition(s) for disk 0". I have read many articles but nobody offered a clear solution for this. Anyone can help me out? Thanks a lot!

Mbr2gpt Cannot Find Os

MBR2GPT.EXE is a tool to help users convert an operating system disk from the MBR to GPT partition style without modifying or deleting any data on the boot disk. You can run it from a Windows Preinstallation Environment (Windows PE) command prompt, or from the full Windows 10 operating system (OS) by using the /allowFullOS option. It is available and located in the Windows\System32 directory on a computer running Windows 10 version 1703 or later.

To convert a system disk with earlier versions of Windows such as Windows 7, 8, or 8.1, you have to upgrade the operating system to Windows 10 first, then perform the MBR to GPT conversion. In particular, Microsoft declared that Windows 11 only supports UEFI, users who need to upgrade their Windows 10 to Windows 11 will have to convert their MBR disk to GPT.

Why MBR2GPT cannot find OS partiiton and how to solve it?

In general, you can use the MBR2GPT command line tool to convert your system disk from MBR to GPT. After this is done, you can boot Windows in modern UEFI mode rather than the old BIOS mode, and you can make the fullest use of 2TB+ hard drive. However, sometimes, it does not work and prompts the error message saying “Cannot find OS partition”. There could be many reasons behind this MBR2GPT conversion failure. One of the most important reasons might be the bad entries in the Boot Configuration data. To solve it, you can refer to the subsequent steps:

Step 1. Make use of diskpart and run the following commands to find out the OS partition and the system reserved partition and assign them a drive letter.

  • diskpart

  • select disk 0: the operating system disk

  • list partition

  • select partition 2: the partition where the Windows OS is installed

  • assign drive letter= w (or other available drive letter)

  • select partition 1: the system reserved partition

  • assign drive letter= b (or other available drive letter)

  • exit: exit the diskpart.exe

Assign Drive Letter

Step 2. Run the command “X: \Sources>dir /a w: \ “to take a further look into the Windows system partition to check whether there are the boot folder inside. If there is not required boot folders, then run the command “X: \Sources>dir /a b: \” to check the system reserved partition.

Find Boot Folder

Step 3. After you find the boot folder in either system partition or system reserved partition, you need to run the “X: \Sources>dir /a b: \Boot” to invoke the bcdedit tool and point it to the boot configuration data store that you have found.

Step 4. Look out the invalid entries now. Run the command: “X: \Sources>bcdedit /store B:\boot\bcd /enum all”. There are many hints for bad or invalid entries. For example, you might find “unknown” in some entry. They can be the remnant of a previous Windows installation or caused by some vicious software.

Check Invalid Entries

Unknown Entry

Step 5. Copy the identifier of the bad entry. Then, point bcdedit to the store again and ask it to delete the bad entry using the copied identifier.

Delete The Bad Entry

Step 6. Then you can try to run the “X: \Sources>bcdedit /store  B:\boot\bcd /enum all” command again to check whether all are OK now.

When everything goes well, try the MBR2GPT tool again. You can make it done successfully this time.

Best way to evade “MBR2GPT cannot find OS partition” problem

Refer to the above solution and you can solve the “cannot find os partitions for disk 0” in MBR2GPT.exe tool. However, it is too complicatd and difficult to follow for most users. So, here we would like to share an easier tool to help you finish the MBR and GPT conversion. That is AOMEI Partition Assistant Professional. Compared with MBR2GPT, it owns the following advantages:

  • Finish the MBR to GPT conversion on an intuitive interface, easy to follow for both experts and newbies;

  • Be able to work well on all editions of Windows 10/8/7 and Windows XP/Vista (32-bit and 64-bit);

  • Support converting both system disk and non-system disk to from MBR to GPT partition styles without deleting any data on the disk.

  • Besides converting disk from MBR to GPT, it can also convert any disk from GPT to MBR, likewise, without modifying disk data.

Now, you can download its demo version for a free trial or simulation.

Try Demo Win 10/8.1/8/7/XP
Secure Download

Important
After the boot disk has been converted to GPT partition style, the firmware must be reconfigured from Legacy BIOS to UEFI.
Make sure that your device supports UEFI before attempting to convert the system disk.

Step 1. Install and run AOMEI Partition Assistant Professional. Right click the system disk and choose “Convert to GPT Disk”.

Convert Disk to GPT

Step 2. In the next window, click “OK” to confirm your operation.

Confirm

Step 3. Back to the main interface, click on “Apply” to commit the pending operation.

Apply

If you want to convert MBR or GPT without loading operating system, you can first use this software to create a bootabale media, then boot computer from it and finish the conversion.

Make Bootable Media

Summary

This page tells how to solve “MBR2GPT cannot find OS partition” on Windows 10. Besides, we also introduce another tool to help you easily get around such issues. The AOMEI Partition Assistant Professional also comes with many other functions: clone MBR disk to GPT disk, or GPT disk to MBR disk, clone partition, transfer OS between MBR and GPT disk, convert dynamic disk to basic disk without deleting volumes, and more. If you are running Windows Server, please switch to the Server edition.