Convert disk from UEFI boot to BIOS boot

Question

I have a disk with a Windows 10 installation on a laptop that has suffered an unfortunate accident. I know the hard disk is still good, and now I'd like to move this disk, including the existing Windows installation, to an older laptop I have sitting around. There are things installed here such that re-installing the OS, applications, and rebuilding my profile on the replacement machine would take a lot of work I'd like to avoid.

Unfortunately, the older laptop does not support UEFI boot/GPT disks. I do know the older laptop runs Windows 10 just fine generally (I've had it on this laptop previously).

Is it possible to convert this disk to Legacy/MBR mode in place, or will I need to re-install Windows? If it's possible, how can I do it?

Answer 1

You'll need to copy the data, convert the disk, copy it back, and then use a recovery tool (I use Macrium personally).

Start by copying your existing partition files to a temporary location, such as an external drive, large flash drive, or different computer.

When that is done, boot off the rescue media and bring up a command prompt. From there, you should be able to use the DISKPART command, select disk for the disk you want to convert, CLEAN it from it's current GPT configuration and run CONVERT MBR. You may also need to specify the file system that you want to use; format fs=ntfs is an example of the command you'd use if you wished to use an NTFS configuration. Create the MSR partition and allocate the size (usually 128MB), with the command:

create partition msr size=128. 

Exit the command prompt after creating that MBR Disk. You should now be able to transfer any existing data, including the Windows OS files you copied previously, back to the partition you just created on the original disk.

Now you can run the recovery utility fully. If your OS boots up, you can check the BIOS version in the start menu, by checking the System Information. It should say "BIOS" if done correctly.

I've run this procedure to convert from BIOS to UEFI, so I'm sure converting from UEFI to BIOS would entail a similar procedure. You might have some boot issues when making this conversion, but I know Macrium provides a tool to automatically resolve this issue as well. Hope this helps.