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From: bointon@kcl-cs.UUCP (Marcus Barnaby Bointon)
Newsgroups: comp.sys.atari.st
Subject: Re: Questions about hardware
Summary: GCR
Keywords: Spectre GCR
Message-ID: <1022@xenon.kcl-cs.UUCP>
Date: 13 Jun 90 08:40:33 GMT
References: <1039@unicorn.WWU.EDU> <1835@lzsc.ATT.COM>
Reply-To: bointon@kcl-cs.UUCP (Marcus Barnaby Bointon)
Organization: Dept. of Computing, Kings College London
Lines: 19

In article <1835@lzsc.ATT.COM> hcj@lzsc.ATT.COM (HC Johnson) writes:
>2. Spectre GCR includes a device to read MAC floppies on the ST drives.
>    This requires roughly 1.44 MB performance from the ST 720 K drives.

  Sorry, this is not true. GCR stands for Group Code Recording and is a form 
of RLL encoding. The hardware problem Dave Small has overcome is that GCR uses
constant data density, and hence it varies the speed of the disk (listen to a 
Mac formatting) to keep this so. The ST drives are not variable speed, so
something like varying the speed of the floppy controller has to be done, which
is very clever. (Congrats. to DS!!) I don't think the spec of the ST drive is 
*too* important (though I would not be surprised if a bad one didn't work) the
capacity is not that much greater and can be accounted for by the use of GCR.

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