Date: Wed, 6 Sep 2006 11:55:17 -0700 From: Chuck Swiger <cswiger@mac.com> To: "Hilt, Ian" <ihilt@mcgregor-surmount.com> Cc: freebsd-questions@freebsd.org Subject: Re: Origin of hard drive parameters Message-ID: <91AFEF09-05EE-41BE-846F-665FBE64EE06@mac.com> In-Reply-To: <890E919AB0857D4A8A52A4AD5E0F0F6221A1C1@msc-server.msc.mcgregor-surmount.com> References: <890E919AB0857D4A8A52A4AD5E0F0F6221A1C1@msc-server.msc.mcgregor-surmount.com>
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On Sep 6, 2006, at 11:40 AM, Hilt, Ian wrote: > Basically, I want to know where the BIOS gets the hard drive > parameters > when the Drive Type is set to "AUTO" in the BIOS configuration. The > 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 > 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 > drive, > or neither? "Neither" is probably the best answer. 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. 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. -- -Chuck
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