Default support for GPT [was: Re: More than 8 labels per slice]

Marcel Moolenaar marcel at
Tue Apr 27 20:39:49 PDT 2004

On Tue, Apr 27, 2004 at 10:08:59PM -0400, Robert Watson wrote:
> > > If there are no objections I'll enable it on i386 and amd64 over the
> > > weekend or so. If people feel we should enable the support on alpha
> > > and sparc64 as well, holler.
> > 
> > I remember there being rumors a year or two ago about Intel trying to
> > sack legacy BIOS and MBR support on x86 entirely and force everyone to
> > use EFI and GPT.  Without GPT support in the system bootstrap, it's not
> > terribly interesting to use except on secondary storage. 
> The GPT partition table includes an fdisk compatibility partition table in
> it to describe the first partition (and reserve the rest?).  That way you
> can boot from an older BIOS even if you lay down GPT over the entire boot
> disk, or at least I believe that was the intent.

Not quite. The MBR on a disk with GPT is expected to be a protective
MBR, which only serves the purpose of marking the whole disk (or as
much as you can cover with the MBR) as used to avoid that MBR tools
trash the GPT disk by thinking there's no data on it. At least EFI
does not support both MBR partitions and GPT, but it is technically
possible to create such a disk. Our GPT code currently allows this,
but this is not by design. It's for convenience. The gpt(8) tool does
not like MBR partitions with GPT, but it could be made less picky.

It's not unthinkable to have bootable GPT on i386 and amd64. New boot
blocks need to be written and we need a way to mark root partitions.

 Marcel Moolenaar	  USPA: A-39004		 marcel at

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