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_at_trailing-edge.com <CLASSICCMP_at_trailing-edge.com>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
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_at_trailing-edge.com
> Trailing Edge Technology WWW: http://www.trailing-edge.com/
> 7328 Bradley Blvd Voice: 301-767-5917
> Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Wed Apr 07 1999 - 20:14:04 BST