[SeaBIOS] GPT disks in a BIOS world
Kevin O'Connor
kevin at koconnor.net
Wed Jun 6 01:09:33 CEST 2012
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
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