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Date:      Wed, 23 Feb 2011 11:33:10 -0500
From:      John Baldwin <jhb@freebsd.org>
To:        freebsd-current@freebsd.org
Cc:        freebsd-arch@freebsd.org, "James R. Van Artsdalen" <james-freebsd-current@jrv.org>, Peter Jeremy <peterjeremy@acm.org>, freebsd-sysinstall@freebsd.org
Subject:   Re: FreeBSD Installer Roadmap
Message-ID:  <201102231133.10571.jhb@freebsd.org>
In-Reply-To: <4D65328D.3050709@jrv.org>
References:  <4D35CFFB.3010302@freebsd.org> <20110222205741.GA34103@server.vk2pj.dyndns.org> <4D65328D.3050709@jrv.org>

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On Wednesday, February 23, 2011 11:15:09 am James R. Van Artsdalen wrote:
> On 2/22/2011 2:57 PM, Peter Jeremy wrote:
> > When that does come, it will probably be driven by BIOS and hardware
> > vendors dropping support for MBR.
> 
> MBR is not a BIOS concept.  MBR is an OS thing.  The BIOS does not care
> or know what kind of partitioning you use, or if you partition at all.

That is mostly true.  There are some SCSI BIOSes that would examine the MBR
and infer what C/H/S geometry the OS was expecting from the MBR.  The
original dedicated disk dummy MBR triggered a divide by zero in one of these
BIOS ROMs.

> A GPT disk with FreeBSD  should boot fine on a quarter-century-old IBM
> PC/AT, until FreeBSD's "don't support 80286" message.

Even a GPT has a legacy MBR (the PMBR) at the front of the disk (it marks the 
entire disk as in use by a special 0xee partition or some such).

-- 
John Baldwin



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