Re: meeting planning
On 01/15/2015 07:41 PM, Thorsten Glaser wrote:
>> Not quite. You won't be able to boot from anything of that unless your
>> firmware supports that.
>
> Only somewhat right. You have to honour the boot protocol supported
> by the firmware, but that is not often coupled to the partitioning
> scheme.
I don't know a single PC BIOS implementation that supports anything
but four primary partitions and booting from the first sector of the
drive that you selected for boot plus extensions like PXE and so
on. Wikipedia mentions that there are some BIOS implementations that
do support GPT but that's rather non-standard:
"Although it forms a part of the Unified Extensible Firmware Interface
(UEFI) standard (Unified EFI Forum proposed replacement for the PC
BIOS), it is also used on some BIOS systems because of the limitations
of master boot record (MBR) partition tables, which use 32 bits for
storing logical block addresses (LBA) and size information." [1]
> The PC BIOS boot protocol is:
>
> “Read the first 512-octet sector into RAM at 07C00h, then jump to
> that address. Keep the drive number we booted from (00h = floppy,
> 80h = hard disc; others usually unsupported) in the DL register.”
Yes, but the first 512 bytes of a GPT partition usually contain
the protective MBR. GPT/EFI uses a boot partition to boot and
not a master boot record which is why the MBR of a GPT disk doesn't
normally contain boot code.
> It *is* true that an EFI firmware cannot normally boot from a
> hard disc with a Sun disklabel. Funnily enough, a PC BIOS *can*
> as long as you put i386 machine code into it to the right places.
I wasn't talking about Sun disklabels, I was specifically talking
about GPT. And my point stands, most standard BIOS implementations
don't know anything about GPT partition tables.
I mean, yes, you can hack your own stuff to get your 486 PC BIOS
somehow boot from a GPT if you manage to squeeze the necessary code
into the MBR, but that wasn't my point. I was talking about the
standard use case.
Adrian
> [1] http://en.wikipedia.org/wiki/GUID_Partition_Table
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913
Reply to: