From owner-freebsd-questions@FreeBSD.ORG Wed Sep 6 20:20:44 2006 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id C784D16A4DE for ; Wed, 6 Sep 2006 20:20:44 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from smtpout.mac.com (smtpout.mac.com [17.250.248.184]) by mx1.FreeBSD.org (Postfix) with ESMTP id 7FA8D43D46 for ; Wed, 6 Sep 2006 20:20:44 +0000 (GMT) (envelope-from cswiger@mac.com) Received: from mac.com (smtpin03-en2 [10.13.10.148]) by smtpout.mac.com (Xserve/8.12.11/smtpout14/MantshX 4.0) with ESMTP id k86KKiQc021861; Wed, 6 Sep 2006 13:20:44 -0700 (PDT) Received: from [17.214.13.96] (a17-214-13-96.apple.com [17.214.13.96]) (authenticated bits=0) by mac.com (Xserve/smtpin03/MantshX 4.0) with ESMTP id k86KKePF013234; Wed, 6 Sep 2006 13:20:41 -0700 (PDT) In-Reply-To: <890E919AB0857D4A8A52A4AD5E0F0F6221A1C2@msc-server.msc.mcgregor-surmount.com> References: <890E919AB0857D4A8A52A4AD5E0F0F6221A1C2@msc-server.msc.mcgregor-surmount.com> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <945DB39F-ECC9-4872-9F5D-EC45BCD439CE@mac.com> Content-Transfer-Encoding: 7bit From: Chuck Swiger Date: Wed, 6 Sep 2006 13:20:39 -0700 To: "Hilt, Ian" X-Mailer: Apple Mail (2.752.2) X-Brightmail-Tracker: AAAAAQAAA+k= X-Language-Identified: TRUE Cc: freebsd-questions@freebsd.org Subject: Re: Origin of hard drive parameters X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Sep 2006 20:20:44 -0000 On Sep 6, 2006, at 1:06 PM, Hilt, Ian wrote: >> The hard disk has an on-board controller which answers the ATA >> "IDENTIFY DEVICE" command with the hard drive parameters used by the >> BIOS, assuming that the BIOS is operating in the legacy C/H/S mode >> rather than the newer LBA mode which uses absolute block numbers. > > Ok. Maybe the better question is: in either case, C/H/S or LBA mode, > where are these parameters stored? At one time, probably on an EEPROM within the hard drive; nowadays, probably nowhere-- the drive controller computes some numbers dynamically depending on whether the C/H/S versus LBA mode jumper is set, or whether the BIOS makes the extended Int13H call to do LBA mode (or whatever the exact mechanism there is).... >> Note that the answer the drive controller gives will normally be a >> fabricated geometry which does not have anything to do with the >> actual geometry of the physical device, in part because drives >> nowadays keep a variable number of sectors per track rather than >> using a CAV layout. > > If CAV == Constant Angular Velocity, I thought this layout stored a > variable number of sectors per track, as opposed to CLV which stores > data at a constant density over the platters. CAV == Constant Angular Velocity. It's the format used by data CD's which gives less storage space but better random access-- tracks near the center have the same # of sectors as tracks on the outside, which means the outer tracks are spread out more; versus CLV, which stores more data on the outer tracks by slowing down the rotational speed to keep a constant density under the heads. -- -Chuck