[Gllug] Fdisk in a pure Linux environment

Richard W.M. Jones rich at annexia.org
Wed Nov 30 10:49:37 UTC 2011

On Wed, Nov 30, 2011 at 12:44:16PM +1300, David L Neil wrote:
> Isn't the "Boot" star (as reported in Fdisk) now only a hang-over
> from MS-Windows, in fact MS-DOS, and thus irrelevant to a pure-Linux
> machine?
> So can it be ignored totally, relying upon setting boot-drive
> priorities in the BIOS?

I'll make three observations:

The BIOS is supposed to simply load the first sector of the hard drive
and jump to it.  In theory the BIOS is not supposed to care about
partitions at all (although theory and some rare BIOSes may differ).

The MS-DOS / Windows boot sector is particularly pathological: It
firstly checks for a bootable partition and loads the first sector
from it.  But it also checks that there are no other bootable
partitions and refuses to continue if there are any.  Why it does this
second check is beyond me, particularly since they've only got ~ 400
bytes to play with.  You need to have exactly one bootable partition
if using the MS-DOS MBR.

The GRUB boot sector of course works completely differently from the
MS-DOS one.  It has a hard-coded list of sectors that it simply loads
from the disk and jumps to.  No bootable partition check at all.


Richard Jones
Red Hat
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