IBM AT Drive Types

[jim stephens]

Entry 15 was set special, so if a setup program wanted to
scan the table, and it could be a different size, it had a marker
to search for.  Everyone skipped it so that you could either use
bios format programs, the IBM AT prep program for a geometry
from 0-14, or a program that was loaded from a floppy with
the disk controller to format the drive.

The explanation claims that the table entry was used to indicate
special parameters, but I recall some bios programs that used
this, and the disks were not very happy to be moved to other
controller types.

Extended tables went from 16-40 usually.  Int 41 is the pointer
to the table.  It can be dumped using dos debug if the machine
is booted in real mode.

I found a nice reference for the old dos stuff here:

http://www.clipx.net/ng/

Jules Richardson wrote:

> On Tue, 2005-07-05 at 20:39 +0100, Tony Duell wrote:
> > I have a BIOS source listing that gives the hard disk parameter tables.
> > It's not the _original_ BIOS (it's the 1985 one), but I think earlier
> > ones just defined fewer drive types. Anyway :
>
> Home come entry 15 was reserved? (and why pick 15?)
>
> cheers
>
> J.