Converting MBR to GPT

When I built my 2200G PC, I used a 4TB drive I won from TechSpot. The Windows installer initialised the drive to MBR, which meant that only 2TB were available. Since I felt that 2TB is enough, I decided to leave that alone at the time.

For those who don’t know, MBR stands for Master Boot Record. It’s an old way to mark where partitions exist on the disk. The newer format is GPT, GUID Partition Table. It not only allows for drives larger than 2TB, but is also more robust, because it stores the partitioning information in more than one place. On the down side it requires a newer PC, with UEFI support (instead of a basic BIOS) and a modern OS (Vista x64 or newer). These aren’t really problems with PCs from the past 10 years or so.

Windows Disk Management can’t convert a drive from MBR to GPT unless it’s empty, and most of the tips Google found were either irrelevant, hard to do or directed to ‘free’ software which didn’t include the functionality in its free version.

Which is why when I finally found the simple solution I figured I’d post. Google did find it, it’s just not the thing that pops up immediately and depends on the search.

Anyway, the solution is MBR2GPT, which already comes with Windows 10. It’s a command line program and it does the job well. Here’s a detailed explanation of how to use it:

  • Click the Start Menu icon (bottom left) and type ‘CMD’ (without the quotes). You’ll get Command Prompt at the top of the search results.
  • Right click Command Prompt and click ‘Run as administrator’. Click ‘Yes’ in the UAC dialogue.
  • You need to know your disk number. If you only have one disk, the number is 0. Otherwise you can find it either in Disk Management (right click the Start Menu icon and select it) or run DiskPart from the command line you just opened, type ‘list disk’ to get a list of disks, and the type ‘exit’).
  • Type ‘mbr2gpt /convert /disk:0 /allowFullOS’. (Replace ‘0’ with the relevant disk number.)

That’s it. Really simple and worked fine for me.

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