Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!hao!oddjob!gargoyle!ihnp4!cbosgd!mandrill!neoucom!wtm
From: wtm@neoucom.UUCP (Bill Mayhew)
Newsgroups: comp.sys.apple
Subject: Re: Apple Drive bashing (Was: noKLICKstart in comp.sys.amiga)
Message-ID: <688@neoucom.UUCP>
Date: Thu, 10-Sep-87 09:11:25 EDT
Article-I.D.: neoucom.688
Posted: Thu Sep 10 09:11:25 1987
Date-Received: Sat, 12-Sep-87 18:17:07 EDT
References: <3905@well.UUCP> <341@remsit.UUCP>
Organization: Northeastern Ohio Universities College of Medicine
Lines: 55
Summary: Apple Head Banger


> why 39 times...?

When the original Apple Disk ][ and it's controller came out, Woz
took a very nihlistic approach.  Years back there was an article
quoting Woz where he patted himself on the back about the
wonderfulness of the Disk ][ and how few parts it had.  By the way,
he claimed that he even did the art work for the PC board himself.

So, the bottom line is that it was essentially a matter of religion
that the Disk ][ didn't have a track zero sensor  Leaving the
sensor out probably saved a flip-flop, inverter gate, and perhaps,
a transistor and a few resistors.  It probably saved $0.50 to $1.00
in the drive itself too.  Now, if they sold 500,000 drives, that
would mean a lot of extra profit, assuming that apple charged
whatever the market would bear in either case-- which they did.

Note that extra money was saved on the original firmware
development too, since there was no need to deal with worring about
the status of the sensor.

What annoyed me was the 5.25 inch Duodisk.  It used relatively
chintzy ALPS (I think) mechanisms that really aren't up to the
pounding of the stepper motor repeatedly at track zero.  The metal
band that attaches the head carriage to the motor also makes a lot
more racket than the plastic sprial used in the older Shugart
drives.  We've had more trouble with the Duodisks.

On some of our Apple // ][ ][+, etc., we've replaced the drives as
they wear out with Nihon Office Corp. Toshiba based drives.  The
Nihon units have an integral controller board that does use a track
zero sensor that prevents them from making the b-r-r-r-r-a-a-t!.
JDR Microdevices sells these drives under the label BAL-500.  See
the back of Byte for further info.

By the way, I think that the head bangs 35 times.  The assumption
is that the head might be on the highest numbered track,
necessitating 33 steps.  I think they throw in a couple of extra
steps to make sure that the follower drops into the sprial groove
in the case of the Disk ][.

I have to give Woz a lot of credit.  The Disk ][ was quite an
Amazing accomplishment of finesse over brawn.  At the time the Disk
][ was introduced around 1979, typical CP/M machines were using
controllers that had 45+ ICs.  The elegance of the Apple design is
very apparent when compared to the kludgey 1541 (also a GCR format)
drive that Commodore brought out a few years later.  I always
wondered why Commodore used their ridiuculous seial bus that made
the disk have an effective data transfer rate of about 300 baud!

Bill Mayhew, Electrical Engineer
Division of Basic Medical Sciences
Northeastern Ohio Universities' College of Medicine
Rootstown (what a name!), OH  44272-9989    phone:  216-325-2511
(wtm@neoucom.UUCP   ...!cbatt!neoucom!wtm)