Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: GCR encoding on amiga
Keywords: What's GCR encoding ??
Message-ID: <14587@cbmvax.commodore.com>
Date: 21 Sep 90 16:53:03 GMT
References: <1411@dnlunx.pttrnl.nl> <429@cbmger.UUCP>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Distribution: comp
Organization: Commodore, West Chester, PA
Lines: 32

In article <429@cbmger.UUCP> peterk@cbmger.UUCP (Peter Kittel GERMANY) writes:

>Provision of GCR on the Amiga is for historical reasons. It was used
>in the old CBM floppies from 2020 to 8250 (did you know that Commodore
>offered already 1983 floppies with 1 MB capacity each on simple DD disks?)
>and on all the C64 compatible floppies. When I'm told correctly, also
>Apple used GCR, perhaps in a slightly different way.

The Apple II used a GCR encoding, which was adapted to the Macintosh at a
higher density.  The GCR capability in the Amiga was originally to permit the
use of Apple II floppy disks.  Which tells you just how long ago work on the
Amiga chips began.  This was in the chips before Commodore bought Amiga.  But
by that time, Apple II compatibility wasn't much of an issue.  Being that
the MFM encoding used is quite a bit simpler to encode/decode, Amiga used that 
format for the standard Amiga disk, even though many different formats are
possible.	

>In the Amiga, there is one caveat with GCR. For hardware reasons it
>must be cut in speed by half and is thus less effective than MFM on
>the Amiga drives. So to my knowledge NOBODY uses it on the Amiga, sad.

Except perhaps "Fruit Friend", or whatever that called that program which 
reads Apple II disks.

>Best regards, Dr. Peter Kittel  // E-Mail to  \\  Only my personal opinions... 
>Commodore Frankfurt, Germany  \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk


-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	Standing on the shoulders of giants leaves me cold	-REM