Origin of hard drive parameters

[Chuck Swiger]

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