From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264911AbTK3N1v (ORCPT ); Sun, 30 Nov 2003 08:27:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264912AbTK3N1v (ORCPT ); Sun, 30 Nov 2003 08:27:51 -0500 Received: from mailhost.tue.nl ([131.155.2.7]:43020 "EHLO mailhost.tue.nl") by vger.kernel.org with ESMTP id S264911AbTK3N1t (ORCPT ); Sun, 30 Nov 2003 08:27:49 -0500 Date: Sun, 30 Nov 2003 14:26:49 +0100 From: Andries Brouwer To: Szakacsits Szabolcs Cc: Andrew Clausen , Apurva Mehta , Linux Kernel Mailing List , bug-parted@gnu.org Subject: Re: Disk Geometries reported incorrectly on 2.6.0-testX Message-ID: <20031130132649.GC5738@win.tue.nl> References: <20031128045854.GA1353@home.woodlands> <20031128142452.GA4737@win.tue.nl> <20031129022221.GA516@gnu.org> <20031129123451.GA5372@win.tue.nl> <20031129222722.GA505@gnu.org> <20031130003428.GA5465@win.tue.nl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 01:10:36PM +0200, Szakacsits Szabolcs wrote: > > On Sun, 30 Nov 2003, Andries Brouwer wrote: > > > Just ask yourself this question: does Windows XP require a bootable > > partition to start below the 1024 cylinder mark? > > Windows NT4 has such a restriction. Not Windows 2000 or XP. > > Wrong: > http://support.microsoft.com/default.aspx?scid=kb;en-us;282191 "Wrong" - what a pessimism. That URL just confirms what I wrote: Windows XP has no such restriction. If you explicitly ask Windows XP to use oldfashioned means, then of course that is your own choice. > > > > Usually booting goes like this: the BIOS reads sector 0 (the MBR) > > > > from the first disk, and starts the code found there. What happens > > > > afterwards is up to that code. If that code uses CHS units to find > > > > a partition, and if the program that wrote the table has different > > > > ideas about those units than the BIOS, booting may fail. > > > Exactly. > > Good. We agree. > > I'm glad also. So what actually [cs]fdisk do with the CHS entries in the > partition table? Ignore them? Might they convert a given partition start to > different CHS units if the partition entry was deleted then recreated at > the same cylinder? Ha, now we are getting down to business. *fdisk evolves in time, so the answer is very version dependent. Let me answer for today's fdisk. Disk geometry is determined as follows (see fdisk.c:get_geometry()) heads = user_heads ? user_heads : pt_heads ? pt_heads : kern_heads ? kern_heads : 255; sectors = user_sectors ? user_sectors : pt_sectors ? pt_sectors : kern_sectors ? kern_sectors : 63; that is, if the user has specified a geometry on the command line, then that is what we use; otherwise, if there is a partition table already and we are able to guess a geometry from that, use that; otherwise, if the kernel has some idea, use that; finally use */255/63 when no information is available. Andries