Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264905AbTK3NOx (ORCPT ); Sun, 30 Nov 2003 08:14:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264907AbTK3NOx (ORCPT ); Sun, 30 Nov 2003 08:14:53 -0500 Received: from mailhost.tue.nl ([131.155.2.7]:31751 "EHLO mailhost.tue.nl") by vger.kernel.org with ESMTP id S264905AbTK3NOv (ORCPT ); Sun, 30 Nov 2003 08:14:51 -0500 Date: Sun, 30 Nov 2003 14:13:14 +0100 From: Andries Brouwer To: Andrzej Krzysztofowicz Cc: linux-kernel@vger.kernel.org (kernel list) Subject: Re: Disk Geometries reported incorrectly on 2.6.0-testX Message-ID: <20031130131314.GB5738@win.tue.nl> References: <200311300220.hAU2K0dr019280@sunrise.pg.gda.pl> <200311300222.hAU2MqcB002434@green.mif.pg.gda.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200311300222.hAU2MqcB002434@green.mif.pg.gda.pl> User-Agent: Mutt/1.3.25i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 30, 2003 at 03:22:52AM +0100, Andrzej Krzysztofowicz wrote: > > The BIOS reads the MBR and jumps to the code loaded from there. > > There is no need for any partition table, or, if there is a table, > > for any particular format. It is all up to the code that is found > > in the MBR. > > I found some PC BIOS-es refuse to read the MBR if no active partition is > found in the partition table... Yes. We are getting a bit away from disk geometries, but it is true that there are many broken BIOSes that in some way depend on partition table format or MBR format. I recall the report that one BIOS tuned IDE modes by reading the MBR and seeing whether it ended with 0xaa55. If not it tried a lower speed. So on a disk without this MBR signature, the I/O would be slow. BSD used to use an entirely different partition table scheme. And it was not uncommon to run a whole-disk BSD system, without any partitioning. Increasingly often that caused problems with broken BIOSes that wanted to interpret partition table contents. The categories of problems that come to mind are: - BIOS has a virus detection option and checks the MBR - BIOS inspects the partition table to find the hibernation partition - BIOS inspects the partition table to find the service partition - BIOS inspects the partition table to guess what geometry it should report I recall that certain Thinkpads would not boot FreeBSD even with a DOS-type partition table because the BIOS did not like the a5 partition ID. So, yes, you are right, practice is much more complicated than theory. Andries - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/