Origin of hard drive parameters
ihilt at mcgregor-surmount.com
Wed Sep 6 13:06:44 PDT 2006
> -----Original Message-----
> From: Chuck Swiger [mailto:cswiger at mac.com]
> Sent: Wednesday, September 06, 2006 2:55 PM
> To: Hilt, Ian
> Cc: freebsd-questions at freebsd.org
> Subject: Re: Origin of hard drive parameters
> 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.
Ok. Maybe the better question is: in either case, C/H/S or LBA mode,
where are these parameters stored?
> 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.
Ian Graeme Hilt
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