How to Migrate OS from MBR to GPT Disk without Boot Issues

Can I convert OS drive from MBR to GPT? Of course! You are in the right place. This guide provides a complete guide on clone MBR disk and conver MBR to GPT without losing data. Why need to migrate OS from MBR to GPT? Here is a typical case:

"How can I migrate a Windows 11 from MBR boot to GPT without reinstalling? o can i convert all my drives to gpt(including OS one) (disk 0 - is hdd where system partition is(i guess) disk 3 is m2, where OS is located) maybe i could somehow move system partition to disk3, but i am not sure will it make some difference." - from Super User

If you want to upgrade Windows 10 to Windows 11, you have to convert system disk from MBR to GPT , clone MBR disk to GPT disk, or clone Windows from MBR HDD to GPT SSD. Continue reading and know the full solution.

Further reading: what is MBR and GPT 

How to Migrate MBR OS to GPT without boot failure

To migrate OS from MBR disk to GPT SSD or HDD successfully, the safest and easiest way is to choose a powerful MBR to GPT migration tool. AOMEI Partition Assistant Professional (suitable for Windows 11/10/8/7/Vista/XP users) provides “Migrate OS to SSD” can migrate OS from one disk to GPT/MBR disk while Windows running. After migration, not only the target disk can be booted, but no data is lost.

In fact, AOMEI Partition Assistant Professional is far more than a migration tool. It is an all-in-one partition disk manager, there are more advanced features you can try. Please download the demo version to see how to migrate MBR OS to GPT disk.

Now, I will demonstrate how to migrate MBR OS from MBR to GPT disk with AOMEI Partition Assistant Professional for you.

Step 1. Preparation for MBR to GPT Cloning

1. Connect or install a second SSD  directly to your desktop or laptop. If your device has only one disk slot, you may need a SATA to USB adapter and cable to connect it.

2. Please check whether your motherboard supports UEFI boot mode and make sure it can be enabled in the BIOS. Otherwise, your PC will not start up normally.

3. Make sure the destination GPT SSD has large enough unallocated space or at least equal size to the original system partition on the source MBR disk. Otherwise, you can shrink or delete other partitions to get enough unallocated space, or shrink the original boot partition to make it easier to fit on the target SSD drive.

4. Convert GPT to MBR: Some users encounter problems - system cloning does not support cloning MBR disks to GPT. After cloning, you cannot boot directly from it. This is mainly because MBR and GPT disks have different boot modes. You need to use AOMEI Partition Assistant to convert GPT to MBR without losing data and this powerful tool will overcome this difficulty and migrate Windows OS from MBR HDD to GPT SSD.

Step 1. Install and launch AOMEI Partition Assistant Professional. Enter the main window, click the disk you want to convert, and select Convert to MBR from the right column.

Step 3. Confirm that you want to proceed by clicking OK. Then, preview the pending operation under ‘Pending Operations’, if you want to proceed click Apply.

Step 2. Begin to Run MBR OS migration

1. Run AOMEI Partition Assistant Professional and you can see all the partitions and disks available. Then select the option “Migrate OS” from the "Clone" feature in the top toolbar.

2. In the next pop-up window, select the unallocated space on the GPT disk as destination location.

3. In the next screen, you can adjust the partition size on the disk if needed and then click “Next”. You can also resize system partition after the migration without data loss.

4. Here comes a note on how to boot from the destination disk. Read it and click on “Finish”.

5. Preview the partition layout and click "Apply" to apply all operations if no problem.

Step 3. Boot from GPT disk

After cloning the MBR OS to GPT disk, you need to change the boot mode from Legacy to UEFI as MBR and GPT have different boot modes:

1. After the computer restarts, long press "F2" or other keys such as DEL to enter the BIOS environment.

2. Change the boot order and set the GPT disk as the first boot device in the BIOS.

3. Change the boot mode from Legacy to UEFI.

4. Then save the changes, and you will successfully boot the OS from the GPT disk.

Why migrate MBR OS  to GPT disk?

Before we know why migrate MBR to GPT, let's know more information about the two types of disks:

▶ MBR is the abbreviation of Master Boot Record, which allows a maximum partition size of 2TB, with 4 primary partitions or 3 primary partitions and 1 extended partition. To create more than 4 partitions on an MBR disk, you should create (up to) 3 primary partitions and then 1 extended partition so that you can create multiple sub-partitions (logical drives).

▶ GPT is the abbreviation of GUID Partition Table. It has no restrictions on partition numbers and disk sizes. GPT system disks can only be booted from UEFI (Unified Extensible Firmware Interface) enabled systems. Only users whose computer motherboards support UEFI can use GPT to create an unlimited number of partitions and take advantage of larger hard drives. However, the GPT structure cannot be used for removable media (USB sticks, CDs, DVDs, etc.).

As you can see, MBR and GPT are two different disk partition styles. But GPT is better than MBR format. It can support 2 TB+ hard drives and contain up to 128 primary partitions.

Besides, GPT disks use UEFI boot mode, which is more advanced than Legacy BIOS for MBR disks. Because UEFI can directly start the operating system after initialization, skip the BIOS self-check process, and finally achieve faster startup. Many users want to migrate MBR OS to GPT disk to enjoy more efficient disk space and faster boot speed.

Summary

This is the whole process to migrate MBR OS to GPT disk and boot from it without any issues. If you have any partition-related issues, or you want to experience Windows 11, then this partition magic will definitely be your perfect assistant. By the way, Windows Server users need to upgrade to AOMEI Partition Assistant Server.