XENIX 2.2.3 and >1024 h.d. cylinder

[uhclem at trsvax.UUCP]

<>
R4>Why did the 1024 limit start? Well, the MSDOS defined partition table
R4>layout only allows 10bit cylinder numbers. So I could see if the

Speaking as someone who has been working with the Western
Digital controllers for at least a year before IBM even knew what one was,
the 1024 limit can be placed squarely on the original controller, the
WD1000, which ran as a simulation of the eventual chip using an 8x300
microprocessor.  These were actually sold!  A lot of them!  The 1010
controller that later reduced this 11" x 8" board down to half that size,
but kept the 1024 limit.  No problem at the time, as the first 70 meg
drive (1024 x 8) did not arrive on the scene until 1984.  Seeing the
limit, Western Digital did produce the 2010, which increased the cylinder
count by one bit (now 2048) cylinders.  (The 2010 is compatible in every
other way with the 1010.)  My company received early 2010
samples (spring '84 I think), which were a bit buggy and since the 70
Meg drive seemed to satisfy the more storage-hungry customers, we elected
not to use it.  The price jump for that extra bit (around $10 more) did
not seem reasonable at the time, particularly since no significant number
of drives that had over 1024 cylinders were even sampling.  Of course, our
systems allowed 4 hard drives on one controller, so the customer had more
upgrade path than 2-drive PCs would allow.

I suspect that when IBM went to Western Digital to have a disk controller
adapter developed, WD selected the less-costly and certainly stable 1010.

Nowdays, newer WD adapter cards like the WA2 have a 2010 controller on
them and it has now become the short-sightedness of the BIOS and O/S
writers for not paying attention to the fact that the 2010 was out there
and that eventually there could even be a 3010.  It was pretty obvious
what WD would do to expand.  There were certainly enough indications to have
made the original AT code so that it would handle the 2010 as an upgrade.
Here is the cylinder registers on a 1010:

		7  6  5  4  3  2  1  0       7  6  5  4  3  2  1  0
	      +------------------------+   +------------------------+
1010 Cntrlr   | x  x  x  x  x  x  9  8 |   | 7  6  5  4  3  2  1  0 |
	      +------------------------+   +------------------------+
		   Cylinder MSB			Cylinder LSB

		x = reserved for future use

And on the 2010, available in a stable form since early 1985:

		7  6  5  4  3  2  1  0       7  6  5  4  3  2  1  0
	      +------------------------+   +------------------------+
2010 Cntrlr   | x  x  x  x  x 10  9  8 |   | 7  6  5  4  3  2  1  0 |
	      +------------------------+   +------------------------+
		   Cylinder MSB			Cylinder LSB

Hmm.  Wonder how they can possibly expand the number of cylinders the
controller supports?  :-(  Well, someone at IBM/Microsoft  (whoever was
irresponsible) didn't see the connection.

If you could sell an incompatible computer these days, this problem would
have been solved the first day.  But, no, we are stuck with the mistakes
made in 1981 and a few new ones in 1985.  Oh, well, so much for innovation.

<My opinion, and not that of my Golden Retriever who is delivering papers
 so he can buy a NeXT, Mac, Amiga, anything that isn't based on a design
 from 1981.>

					"Thank you, Uh Clem."
					Frank Durda IV @ <trsvax!uhclem>
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