[SeaBIOS] GPT disks in a BIOS world

[Kevin O'Connor]

On Tue, Jun 05, 2012 at 11:39:35PM +0700, Ivan Shmakov wrote:
> >>>>> Kevin O'Connor <kevin at koconnor.net> writes:
> >>>>> On Tue, Jun 05, 2012 at 10:58:43AM +0200, Fred . wrote:
> 
> […]
> 
>  >> But does GPT disks even have a MBR?  Isn't the GPT a replacement for
>  >> MBR?  If the disk doesn't have any MBR, does the BIOS load the first
>  >> sector of GPT?
> 
> 	To note: FreeBSD's version of “protective MBR” (pmbr.s) has the
> 	support for GPT and will load the “big” bootloader from a GPT
> 	partition of a specific type.
> 
>  > I'm not sure how I could be more clear on this.  SeaBIOS cares nothing
>  > about the partition table.
> 
> 	Not even about the 0x55 0xAA magic?

SeaBIOS does check that the last two bytes of the first disk sector is
0xaa55 before executing code there as a sanity test.

>  > No BIOS spec (that I'm aware of) requires the BIOS to care anything
>  > about the partition table.
> 
> 	The problem is that the BIOS specs are currently being replaced
> 	with the new UEFI ones, and UEFI boot sequence may be much more
> 	complex (but, AIUI, even in the simplest case, it has to support
> 	the MBR and GPT partition schemes, /and/ the FAT family of
> 	filesystems.)

UEFI is very complex.

I've seen companies push UEFI as a requirement for >2Terabyte drives -
but that's really not true.

-Kevin