Apple GCR - test-drb@ccmp.vtda.org

7 Apr 1999

This is one of APPLE & wierd Woz's patents.  It's in almost every well
equipped electrical engineering library.  There's also an ANSI standard for
GCR as applied by the 9-TRACK TAPE people to get up to 6250 bpi, which will
shed some light as well, should you choose to look it up.  I used that
information to lay a groundwork for my APPLE HDC, which never made it to
market.

Dick

-----Original Message-----
From: CLASSICCMP(a)trailing-edge.com &lt;CLASSICCMP(a)trailing-edge.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Wednesday, April 07, 1999 7:12 PM
Subject: RE: Apple GCR

...
  Can someone
explain how the Apple II GCR worked? I tried deciphering this
several years ago and I could figure it out (the only references I found
were very vague). 
There's one reference which is extremely non-vague: _Beneath Apple
DOS_, by Don Worth and Peter Lechner.  In it you'll find wonderful
illustrations featuring Sir Isaac Newton and leading you through the
wonderfully intertwined world of the Disk ][ state machine, 6502
machine code, and modulation formats.  This book is still available
new (see my past posts to comp.sys.apple2 for details on how to buy it.)

If you're too cheap to buy the book (again, buy the book!  It's
worth every last cent!), the relevant section of it (minus the
cute drawings) is online at

http://www.umich.edu/~archive/apple2/misc/hardware/disk.encoding.txt

But, again, buy the book!  Woz is not my super-hero, but he could do
amazing things with a half-dozen TTL chips, that everyone else was
doing with a hundred or more...

--
 Tim Shoppa                        Email: shoppa(a)trailing-edge.com
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