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Date:      Mon, 20 Nov 2000 17:37:39 +0200 (SAST)
From:      Robert Nordier <rnordier@nordier.com>
To:        stable@FreeBSD.org
Subject:   Re: Dedicated disks (was: Dangerously Dedicated)
Message-ID:  <200011201537.RAA25621@siri.nordier.com>
In-Reply-To: <20001120192044.Q58333@echunga.lemis.com> from "Greg Lehey" at Nov 20, 2000 07:20:44 PM

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Greg Lehey wrote:
 
> > Why do you *insist* on calling it a "Microsoft partition table"??
> 
> Hmm.  I was going to say "Because it was introduced with Microsoft
> 2.0", but I'm no longer so sure.  Reading the MS-DOS 2.11 source code,
> it seems that they didn't have a partition table at the time.

Of course they had a partition table at the time, and of course
MS-DOS 2.11 used it:

    [io.sys]
    1431  8d9fbe01  lea bx,[bx+0x1be]
    1435  8b4740    mov ax,[bx+0x40]
    1438  3d55aa    cmp ax,0xaa55
    143b  7539      jnz 0x1476
    143d  b90400    mov cx,0x4
    1440  807f0401  cmp byte [bx+0x4],0x1
    1444  7407      jz 0x144d
    1446  83c310    add bx,byte +0x10
    1449  e2f5      loop 0x1440
    144b  eb29      jmp short 0x1476

> Can anybody remember when it was introduced?

In March 1983, with the release of PC-DOS 2.0.
 
> Anyway, it's needed for "modern" Microsoft offerings, and not really
> for much else.  It's also not a UNIX partition table.

Actually, the immediate reason for its introduction was in order to
support dual-booting XENIX (Early SCO/Microsoft UNIX) on PCs.  This is 
why the partition type numbering starts

    1  DOS
    2  XENIX
    3  XENIX

-- 
Robert Nordier

rnordier@nordier.com
rnordier@FreeBSD.org


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