Date: Wed, 6 Sep 2006 16:06:39 -0400 From: "Hilt, Ian" <ihilt@mcgregor-surmount.com> To: "Chuck Swiger" <cswiger@mac.com> Cc: freebsd-questions@freebsd.org Subject: RE: Origin of hard drive parameters Message-ID: <890E919AB0857D4A8A52A4AD5E0F0F6221A1C2@msc-server.msc.mcgregor-surmount.com> In-Reply-To: <91AFEF09-05EE-41BE-846F-665FBE64EE06@mac.com>
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> -----Original Message----- > From: Chuck Swiger [mailto:cswiger@mac.com]=20 > Sent: Wednesday, September 06, 2006 2:55 PM > To: Hilt, Ian > Cc: freebsd-questions@freebsd.org > Subject: Re: Origin of hard drive parameters >=20 > On Sep 6, 2006, at 11:40 AM, Hilt, Ian wrote: > > Basically, I want to know where the BIOS gets the hard drive =20 > > parameters > > when the Drive Type is set to "AUTO" in the BIOS=20 > configuration. The =20 > > best > > I've been able to come up with from the internet is an "IDENTIFY" > > command that purportedly > > (<http://www.linux.com/howtos/Large-Disk-HOWTO-10.shtml>) gets its > > information from the "IDE controller". This does not answer my =20 > > question > > completely. Are the parameters returned by the controller hard coded > > into a chip on the board or are they on the platters of the hard =20 > > drive, > > or neither? >=20 > "Neither" is probably the best answer. >=20 > The hard disk has an on-board controller which answers the ATA =20 > "IDENTIFY DEVICE" command with the hard drive parameters used by the =20 > BIOS, assuming that the BIOS is operating in the legacy C/H/S mode =20 > 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? =20 > Note that the answer the drive controller gives will normally be a =20 > fabricated geometry which does not have anything to do with the =20 > actual geometry of the physical device, in part because drives =20 > nowadays keep a variable number of sectors per track rather than =20 > using a CAV layout. >=20 If CAV =3D=3D 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. Ian Graeme Hilt
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