It might be interesting to dig up some old posts from ubuntu-mate.community.
First of all, @lah7 's warning
For a BIOS machine, the most compatible and simplest solution is to use a MBR formatted disk. GPT may have worked, but it’s a hit-and-miss and I don’t think it’s worth the trouble. Booting from a GPT drive is geared more for towards a (U)EFI system.
Also, I tried this some time ago on some BIOS machines and I would advise against using GPT on old BIOS. It is not worth the trouble.
In my experience it is indeed ‘hit and miss’ because BIOSss that don’t follow the BIOS standard will fail to boot, and quite some BIOSes do not adhere to the standard. (SONY is notorious in that aspect)
In that thread I also linked to this which does a good explanation about the why and how.
Here an excerpt:
The BIOS generally doesn’t care anything about your hard drives. It simply loads the MBR and transfer control to the boot loader in MBR. Therefore technically it’ll be possible to boot a GPT drive in BIOS mode, because the GPT drive still has a protective MBR at the beginning. You just need a bootloader that supports GPT disks (such as Grub and many other Linux bootloaders)
However, here a small problem arises. On MBR drives the boot loaders often cheat a bit by storing a part of them in the next sectors called “MBR gap”, “boot track”, or “embedding area” which are often left empty by disk partitioning tools. On a GPT disk the sectors right after the MBR are GPT data structures, hence can’t be used for that purpose and you need to create a small BIOS Boot Partition for Grub to store its data.
Some more things I experienced can be found here: