Convert to UEFI - reinstall windows?

Styxx · August 8, 2020

I built myself a new PC last week. (Parts list is here: https://uk.pcpartpicker.com/user/Styxx1000/saved/m8HNcf, although I'm not sure that's much use for this issue) Today I realised that I've installed Windows on an MBR partitioned drive (NVMe Samsung 970 Evo Plus). This is my first build so there's a certain amount of learning for me here, basically I hadn't realised that this was a thing. I found another thread saying that UEFI needs the drive to be GPT partitioned. Also, this link was provided to convert: https://www.windowscentral.com/how-convert-mbr-disk-gpt-move-bios-uefi-windows-10

My main question is, is there any downside to converting the drive in this way, or would it be better for me to do a clean install of Windows? I've not done anything serious with the PC so far, so a clean install won't screw me, but if I can avoid having to set up everything again then that would be great. If I do need to re-install, am I likely to run into any issues with the Windows license key? Bearing in mind that I've already used it once, albeit on the same machine.

Also, to convert to UEFI I have found two sections in the BIOS that mention UEFI, please see attached pictures. I think that I need to set the first one to UEFI, and that I can leave the second on LEGACY+UEFI. Is that correct?

Many thanks to anyone who takes the time to read and reply.

BobVonBob · August 8, 2020

That link will work fine, but honestly I'd say just leave it as is. The primary reason to use GPT is if you have a drive larger than 2 TB, and even then the partition scheme of your OS drive doesn't matter as long as the >2 TB disk is GPT.

Styxx · August 8, 2020

19 hours ago, BobVonBob said:

That link will work fine, but honestly I'd say just leave it as is. The primary reason to use GPT is if you have a drive larger than 2 TB, and even then the partition scheme of your OS drive doesn't matter as long as the >2 TB disk is GPT.

Thanks. Is that the only real benefit then? I thought it was supposed to perform better under UEFI.

BobVonBob · August 8, 2020

32 minutes ago, Styxx said:

Thanks. Is that the only real benefit then? I thought it was supposed to perform better under UEFI.

It might boot a few seconds quicker with UEFI, but other than that there's absolutely no difference in your case. Once you're booted MBR (BIOS) and GPT (UEFI) perform identically.

There is a very heavy performance hit (near 75% performance loss) for using GPT if you have very old hardware that wasn't built to support GPT, but that's a nonissue here.