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From: John Baldwin <jhb@freebsd.org>
To: Marcel Moolenaar <xcllnt@mac.com>
Date: Tue, 16 Jun 2009 13:17:21 -0400
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Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org,
	src-committers@freebsd.org, Bruce Evans <brde@optusnet.com.au>,
	Ulf Lilleengen <ulf.lilleengen@gmail.com>
Subject: Re: svn commit: r194241 - head/lib/libdisk
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On Tuesday 16 June 2009 12:45:21 pm Marcel Moolenaar wrote:
> 
> On Jun 15, 2009, at 11:33 PM, Ulf Lilleengen wrote:
> >
> > I'm a bit confused now :)
> 
> What bde@ said is that 255 is the max number of heads that is
> supported everywhere. 256 may work but is not always
> supported. Some web page states that DOS and Windows 95/98
> don't support 256 heads(1).
> 
> (1) http://web.inter.nl.net/hcc/J.Steunebrink/bioslim.htm#4GB

There was a bug in the BIOS for 2940 Adaptec SCSI controllers IIRC where it 
would actually hit an internal divide-by-zero bug if it encountered an MBR 
table with an entry where the head was 255 (it did a + 1 to get the number of 
heads so it could work out C/H/S the MBR was expecting).

-- 
John Baldwin