Re: Origin of hard drive parameters

From: "stheg olloydson" <stheg_olloydson@xxxxxxxxx>
On 9 Sep 2006 14:54:09 -0000 ihilt wrote:

On Wednesday 06 September 2006 7:54 pm, jdow wrote:

>> Ok. Maybe the better question is: in either case, C/H/S or
LBA mode,
>> where are these parameters stored?

They flat out are not stored anywhere. There is a standard
algorithm
published by the VESA people, I believe, that provides the
data for
all SCSI drives and modern IDE/ATA/SATA drives.

Do you know the name of this standard or where I can get it?

Ian Graeme Hilt

Actually, the stardard is created by the T13 Technical Committee

And my idle curiosity would like to know why Ian is interested in
such an antiquated topic? There is a size limit beyond which CHS
simply does not work. The setting of CHS is in practice utterly
arbitrary. For (many/most?) USB ram disk plugins the T13 standard
does not apply due to internal ram layout. And so forth.

(Certainly on the Amiga this CHS nonsense made no practical
difference except on floppy disks or ST-506 based disk drives. And
in playing with recovering a blown block zero on an Windows machine
(more than once) I learned that CHS is utterly arbitrary on Windows.
It is arbitrary with USB ram disk modulo the ram disk's internal
layout and spares setup. And since large disks for which CHS runs
out of size abound I imagine there is not a place in the 'n'x world
where CHS matters. So I am suspecting historical curiosity if
anything else. As for storing it - read block zero of the disk.
Be DAMN careful not to WRITE to block zero. And if you DO write
to block zero at about the time I quit doing such low level stuff
and moved to other things there were several SCSI hard disk manufacturers using code that had a defect such that if you wrote
more than one disk block starting at block 0 the whole disk was
toast until you did a fresh low level format on it. One sincerely
hopes THAT defect is gone these days.)

{O.O} Joanne
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