Can't install Windows on a second partition due to the disk format being GPT, what's going on?
I want to have 2 Windows 10 installations side by side, so I shrunk my current installation to make space for the second one. I have a hard drive of 1.2TB and currently it has 3 partitions:
- 100MB EFI System Partition.
- 292GB Windows 10 C: NTFS partition
- 824GB Unallocated
- 500MB Recovery partition
When I try to install on the unallocated space, whether I leave it unallocated or I create an NTFS partition, I get the same error:
Windows cannot be installed to this disk. The selected disk is of the GPT partition style
Any ideas what's going on? Why can't I install on a GPT hard drive?
I believe I have solved this but I'm not 100% sure about my solution. When booting from the USB install media, the BIOS boot menu had many options. When I went into the boot configuration and changed CSM compatibility from enabled to auto, which apparently controls GPT vs legacy booting for various different sources (SATA, PCI, network, USB), and rebooted, the boot menu had way fewer options. It actually only had two: my current Windows 10 install and USB. I selected USB and it worked.
My hypothesis is that I was booting from my USB install media in legacy instead of GPT mode and that when I disabled everything but GPT, I booted in GPT. I bet I could have just selected another of the many options I had to boot USB in GPT mode instead of legacy mode, without having to change the BIOS setting, but that didn't occur to me.
This video inspired me to try that: https://www.youtube.com/watch?v=agV0RbIS2bk