From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758277AbYDVULa (ORCPT ); Tue, 22 Apr 2008 16:11:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751874AbYDVULW (ORCPT ); Tue, 22 Apr 2008 16:11:22 -0400 Received: from el-out-1112.google.com ([209.85.162.181]:29316 "EHLO el-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750924AbYDVULU (ORCPT ); Tue, 22 Apr 2008 16:11:20 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=DBVjniJWLT+nGKWHTZC/5bM0sKlaCAgEJCYrIiCE86tfGTiOPBihGgUVFIWWDFI1rou4cAceTJfu1eQyNBHAM3NnLLcgvS7k+YUg1NYtOnbWow7K/Zw16SAPDd4v+b5T9s8RYkm483UNpZ/6Ye7cwkjIJHaRNTlHdmJ84xHILQA= Message-ID: <38b2ab8a0804221311u12fd2209l1fe71c99779eb6fa@mail.gmail.com> Date: Tue, 22 Apr 2008 22:11:13 +0200 From: "Francis Moreau" To: "Seewer Philippe" Subject: Re: Disk geometry from /sys Cc: "Mark Lord" , linux-kernel@vger.kernel.org In-Reply-To: <4808A409.3080406@bfh.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <38b2ab8a0804091353h3725ce29s196e27e8b4f1ff56@mail.gmail.com> <480354C9.1050600@bfh.ch> <38b2ab8a0804150040i14840a9fudc3b95ba80d52ac1@mail.gmail.com> <4805AF93.90209@bfh.ch> <38b2ab8a0804170709m58830adagcba46f059ed10809@mail.gmail.com> <4807635E.9060101@bfh.ch> <4808A09B.6090106@rtr.ca> <4808A409.3080406@bfh.ch> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 18, 2008 at 3:37 PM, Seewer Philippe wrote: > > Mark Lord wrote: > > > That can sound a bit misleading. The complete story, for ATA/SATA drives, > > is that the disk has two geometries: an internal physical one, with a > fixed number of heads and cylinders, but variable sectors/track > > (which normally varies by cylinder zone). > > > > Software *never* sees or knows about that geometry, so ignore it. > > > > The second geometry, is the one that the drive reports to software > > as its "native" geometry. This is what you see from "hdparm -I" > > and friends, and this geometry is what has to be used by software > > when using cylinder/head/sector (CHS) addressing for I/O operations. > > The hardware interface has a limit of 4-bits for the head value, > > so the maximum number of heads can never be more than 16. > > > > Nobody uses CHS addressing for I/O operations, at least not on > > any hardware newer than at least ten years old, so this geometry > > is also unimportant for most uses. > > > > That's what the drive knows about. > > > > Software, for compatibility with the MS-DOS partition table scheme, > > sometimes uses a "logical" geometry, where we "pretend" that a drive > > can have up to 255 heads, which then allows more of the disk to be > > described within the limitations of the partition table data layout. > > That's where one frequently sees "255 heads", even though the drive > > underneath uses 16 at the interface level, and probably as only 2 > > or 4 real heads inside the shell. > > > > Aye. Though I prefer the term virtual geometry. But thats cosmetics. Sorry > for beeing unclear, and many thanks for untangling my post. > > If anyones interested in even more Details about C/H/S adressing and so on, > there's a very good document about that to be found here: > http://www.mossywell.com/boot-sequence/ > unfortunately this link doesn't work for now... -- Francis