3b2 disk limit

[Steve Friedl]

Greg Woods writes:
> Also, to the rest of you 3B2 users:  DON'T change the sector size.
> The firmware only knows about 512b sectors.  This wouldn't be a
> problem if the firmware only loaded the first sector of track 0, but
> it seems the sanity track seems to be elsewhere, and the disk sanity
> check fails instantly.  Now, this may still be possible, but I don't
> know enough about the undocumented drive type id's, and such, nor have
> I looked to see exactly what is stored in sector 0, track 0.

First, there are no "undocumented drive types".  These are just
numbers, and you can get the meaning of all of them by doing an
edittbl command (with args that I don't recall at the moment).
None of them are magic.

Now for more info about sector 0 track 0.  When you format a
drive, the first two cylinders are taken away from you and used
for lots of stuff: bad block tables, error logs, plus the
physical description sector.  The pdsector is (0,0), and it
contains the drive's geometry.

These are normally hidden from your view -- you can't get at them
via normal reads and writes -- but special ioctls will let you
get at them without too much trouble.  Somewhere I have a program
that prints out everything found in the early part of the drive,
and I'll post it if I get enough requests. 

     Steve

-- 
Stephen J. Friedl, KA8CMY / Software Consultant / Tustin, CA / 3B2-kind-of-guy
+1 714 544 6561 voice   /   friedl at vsi.com   /   {uunet,attmail}!mtndew!friedl

"AT&T computers - we're not THAT bad" - Bob Kavner