Accidentally Initialized Disk to MBR? Convert to GPT without Data Loss!

Sometimes, you might accidentally initialized disk to MBR. But don’t worry, you can use the AOMEI Partition Assistant software to convert the MBR disk to GPT without deleting any existing partitions or losing any data on the disk.


By Emily / Updated on May 12, 2023

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Accidentally initialized disk to MBR!

“I have a 4TB external hard drive and accidentally initialize the disk to MBR, then I can just use only 2TB, and the rest 2TB shows unallocated space, cannot be used to create a new partition, either. So, i want to convert it to GPT and make the fullest use of the 4TB disk space. But i don’t want to lose the existing data on the MBR disk, any way to realize it? Thanks! ”

Difference between MBR and GPT: Should you initialize disk as MBR or GPT?

Before partitioning and formatting a drive for data storage, you will be required to initialize disk to MBR or GPT. They are two different partition styles and differ a lot in the following aspects, which helps you determine whether to initialize disk as MBR or GPT:

  • Max Disk Size: MBR disks only support up to 2TB disk size, once the size surpasses 2TB, the excess part cannot be read or displayed. However, GPT disks are capable of a maximum of 18EB partition.

  • Max Primary Partition Numbers: MBR disk only allows 4 primary partitions at most, if more primary partitions are required, you have to build a secondary structure known as extended partition, and then you can create numerous logical partitions inside. However, a GPT disk can contain 128 primary partitions.

  • OS Compatibility: All editions, except Windows XP 32 bit, can read and use GPT for data storage, but only 64-bit Windows (starting from Windows Vista) are system compatible with GPT-based disk. Both all 32-bit and 64-bit Windows versions are data and system compatible with MBR.

  • Boot Mode: The MBR uses Legacy BIOS boot while GPT adopts UEFI boot. If your computer’s motherboard supports Legacy mode only, you can only boot Windows from MBR disk. Similarly, if the motherboard supports UEFI mode only, you can only boot OS from GPT disk.



Easy steps to convert MBR disk to GPT without data loss

When you accidentally initialize disk to MBR, it is risky to convert it to GPT via Windows Disk Management and DiskPart since both methods only support converting an empty disk between MBR and GPT. Namely, if the disk that is initialized to MBR accidentally contains any partitions and data, you have to delete all of them before conversion. In such a case, it is necessary to back up vital data in advance.

To convert MBR to GPT without deleting partitions and losing data, it is recommended to use the AOMEI Partition Assistant Professional. This partition manager can directly convert either data disk or system disk to MBR or GPT with keeping the existing partitions safe. So, if you accidentally initialize external or internal hard drive to MBR, you can use it to convert disk to GPT securely.

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Step 1. Install and launch AOMEI Partition Assistant Professional. Right-click the disk and select “Convert to GPT”.

Convert 3tb Mbr Disk To Gpt

Step 2. Click “OK” to confirm your operation.

Ok 3tb Disk

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

Apply 3tb

☞For conversion between MBR and GPT disks on the laptop, please make sure the power supply is sufficient.
☞To ensure the data is consistent, do not abnormally terminate the program during the conversion process.
☞To convert system disk from MBR to GPT, please ensure your computer’s motherboard supports UEFI boot mode since you have to change Legacy BIOS to UEFI after conversion.


So, if you accidentally initialize disk to MBR, the AOMEI Partition Assistant Professional can help convert it to GPT easily and securely. Besides, it is capable of finishing many other conversion tasks, like converting logical drive to primary drive without losing data, converting dynamic disk to basic disk without data loss, and converting file systems between NTFS and FAT32 without reformatting. If you are running Windows Server, please switch to the Server edition.

Emily · Staff Editor
Emily is an English editor of AOMEI Technology; she has a great passion for providing easy solutions for people to tackle with all disk or partition management problems. In addition to writing articles about disk/partition management, she also edits great tutorials on how to back up and restore disk for data security. In her spare time, she loves to learn computer skill to improve herself or stay with her family to enjoy a good day.