Date: Mon, 20 Nov 2000 12:23:02 -0800 (PST) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: imp@village.org (Warner Losh) Cc: bfoz@glue.umd.edu (Brandon Fosdick), Cy.Schubert@uumail.gov.bc.ca (Cy Schubert - ITSD Open Systems Group), stable@FreeBSD.ORG, roelof@eboa.com (Roelof Osinga) Subject: Re: Dangerously Dedicated Message-ID: <200011202023.MAA19454@gndrsh.dnsmgr.net> In-Reply-To: <200011192210.eAJMAWG03651@billy-club.village.org> from Warner Losh at "Nov 19, 2000 03:10:32 pm"
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> In message <3A180EA0.31926227@glue.umd.edu> Brandon Fosdick writes:
> : So we're going to be stuck with MS style partitions on machines that only run
> : FreeBSD? I don't like this idea.
>
> First, these aren't MS style partitions. They are part of the PC
> spec. FreeBSD is lying to the BIOS with the MBR that we put onto the
> disk, and that causes problems.
Seems people are getting very confused here about what the BIOS cares
about and what cares about the partition table, what the specs say and
what software is actually doing what.
The original IBM AT spec could give a rats ass about a partition table,
all that it cares about is the boot block signature (magic 0xAA55). It
is the MBR that knows what a partition table is and how to deal with it.
The original spec says if there is a valid signature, load the code and
jump to it passing the drive number in reg dl so that the boot code knows
where it was loaded from. It was up to the MBR to decide what to do from
then on.
Note that some newer BIOS's have violated the original spec and intent
by now looking at the partition table, bad BIOS, bad bad bad BIOS (typically
oem's like gateway, compaq, dell, HP). Also note that most current BIOS's
actually do follow the original spec and work just fine (Award, and non-oem
modified Phoenix).
Almost all partitioning tools assume that if there is a boot signature a
DOS style partion table exists in the MBR, technically this software is
in error.
So in summary:
a) The BIOS knows about a boot signature and what to do with it,
it should not know about a partion table, if it does it is
technically broken.
b) The MBR knows about partition tables, if it cares about them.
c) Software that assumes there is a partition table just becuase
there is a boot signature is technically broken, but quite common.
> Second, the amount of space wasted is nearly 0 (32k on most IDE disks,
> 64k on scsi).
The wasted space is exactly 1 track - 1 block.
--
Rod Grimes - KD7CAX @ CN85sl - (RWG25) rgrimes@gndrsh.dnsmgr.net
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