8 Apr
1999
8 Apr
'99
4:39 p.m.
You're right in that it would be silly to bang the head assembly into
anything. I didn't say they did that, though it would work for a while,
maybe. It's clear to me that Apple drives do things differently from other
drives just from listening to them when the machine starts up. I'd never
pretend to "know" what they do. In fact I'd be hesitant to admit it if I
did know. Your observation that there were alignment problems with Apple
disk drives sounds familiar too. Could it be that they actually did bang
the head into the stops?
My contempt for Apple begins and ends with their total disregard for the
value of your data. If you wrote to their floppies, especially if your
computer was in the "front room" of a business, exposed to whatever dust was
carried in by customers and wind, etc, from the parking lot, (I had a client
years ago, whose mail-order business was operated with the "help" of an
Apple-II with two controllers and three drives in just such a location.)
you'd frequently observe the computer locking up because it had come to a
bit it couldn't read. The reason was probably contamination of media or
drives, but the only recovery was the reset. Your data, meanwhile, and
perhaps your customer calling long distance, were gone by now. They
designed the MAC with no memory parity assuming that you'd not mind if your
data was corrupted without your knowledge, and though the disk handling was
a bit more mature than the Apple-II "I give up . . . and die" it wasn't
much
better.
I've never taken note of the 8" drives' sensor for track 43. I always
believed that since they had provided a "low-current" control on the
interface cable, it was not necessary. I suppose I'd have taken note if one
had failed along the way. Of the many dozens of 8" drives I've owned, I
never had one fail. I used several of these for 7 or 8 years, moving them
about and just generally abusing them, yet they seemed to keep going. I
only occasionally aligned a drive for someone else, or as part of a checkout
of an "experienced" set of drives we were buying. The only drives which
ever gave a noticeable amount of trouble were the Persci. They were "hangar
queens" of the first order. I had a couple of those for a time because I
had to verify they worked properly with our controllers.
Dick
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Thursday, April 08, 1999 8:50 PM
Subject: Re: stepping machanism of Apple Disk ][ drive (was Re: Heatkit 5
1/4 floppies)
Actually there are two points. One is track 000 and the other is the
innermost (for sa400 35-40 tracks later). Only track 000 was sensored
save for apple didn't use that either. Apple cut the interface to the
A very silly nitpick:
I have an 8" drive here with 2 slotted optoswitches on the head carriage.
One is on track 0. The other is on track43 and all later tracks. The
reason for the latter one? It automatically does the write current switch
at track 43.
minimim number of wires and signals possible and
made up the difference
with software, rather clever in my mind.
And rather silly in my mind. Continually banging the head into the end
stop does cause the alignment to drift. I've had plenty of Disk IIs and
1541s (another drive that seems to bang the head rather too much) in for
repair. Often alignment is the problem.
Allison
-tony