Path: utzoo!utgpu!water!watmath!clyde!ima!cfisun!lakart!dg
From: dg@lakart.UUCP (David Goodenough)
Newsgroups: comp.periphs
Subject: GCR (was Re: RLL: ..... )
Message-ID: <116@lakart.UUCP>
Date: 17 May 88 15:52:45 GMT
References: <11508@mimsy.UUCP>
Organization: Lake - The systems people
Lines: 17

From article <11508@mimsy.UUCP>, by chris@mimsy.UUCP (Chris Torek):
>>... 2,7 RLL is a variable length code (e.g. 0011 maps to 00001000 but
>>010 maps to 100100); I don't have a simple formula for the 2,7 RLL code!
 
So where do we draw the line between GCR (group code recording) and RLL?
I was under the impression that GCR does a similar thing to RLL in that it
takes (say) 4 bit patterns and expands them to (say) 5 or 6 bit patterns
on the disk. I have always heard GCR described as self-clocking, for the
reason that it does not require "explicit" clock pulses a la FM or MFM,
instead the data pulses are never far enough apart to cause a loss of sync.

	Just my $0.02 worth!!
-- 
	dg@lakart.UUCP - David Goodenough		+---+
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