From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: util-linux-owner@vger.kernel.org Received: from avasout04.plus.net ([212.159.14.19]:34839 "EHLO avasout04.plus.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751562Ab2GZAjT (ORCPT ); Wed, 25 Jul 2012 20:39:19 -0400 Message-ID: <50109E8D.2000702@jelmail.com> Date: Thu, 26 Jul 2012 02:34:05 +0100 From: John Lane MIME-Version: 1.0 To: util-linux@vger.kernel.org Subject: fdisk geometry Content-Type: text/plain; charset=ISO-8859-1; format=flowed Sender: util-linux-owner@vger.kernel.org List-ID: Hello, I'm in the middle of studying disk organisation to enhance my understanding in this area. I have a few questions about fdisk (trying to fill a gap in my knowledge if that's ok)... In the below output of fdisk it shows (correctly) a geometry of 224 heads, 56 sectors/track. I'm unclear about where this information comes from. Normally a disk's geometry would be reported as 255 heads and 63 sectors. I explicitly partitioned this disk using a 224/56 geometry, so the report is correct. I'd just like to understand: (a) where fdisk gets the information about the geometry from in this specific case? (b) when fdisk defaults to 255/63 is that because it's hard coded that way or is there another reason? I understand why it's 255/63 by default but haven't been able to understand how the geometry is determined. I do know that it's all kind of moot these days anyway because of sector based addressing but that leads to one other question: given sector based addressing why does fdisk even bother displaying a geometry any more ? Doesn't it just serve to confuse? # fdisk /dev/sda Welcome to fdisk (util-linux 2.21.2). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): p Disk /dev/sda: 80.0 GB, 80026361856 bytes 224 heads, 56 sectors/track, 12460 cylinders, total 156301488 sectors Units = sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0xc4c4122e Device Boot Start End Blocks Id System /dev/sda1 * 56 501759 250852 83 Linux /dev/sda2 501760 156298239 77898240 8e Linux LVM Command (m for help): q Many thanks for your time, John Lane.