Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!cbmehq!cbmger!peterk
From: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Bizarre Fantasy: RLL Flopies?
Keywords: MFM, RLL, Floppies, Blitter, Clueless, Fantasy, etc.
Message-ID: <1034@cbmger.UUCP>
Date: 2 Apr 91 16:34:59 GMT
References: <1991Apr2.061633.17980@kessner.denver.co.us>
Reply-To: peterk@cbmger.UUCP (Peter Kittel GERMANY)
Organization: Commodore Bueromaschinen GmbH, West Germany
Lines: 28

In article <1991Apr2.061633.17980@kessner.denver.co.us> chris@kessner.denver.co.us (Chris Hanson [Lord Xenon]) writes:
>
>  I was scamming the Hardware manual the other day, looking for ways to
>improve that audio quality. But that's not what I'm posting about. I noticed
>that trackdisk.device uses the blitter to encode data into raw MFM codes,
>and back. Now, it's a simple leap of faith to wonder if therefore we
>couldn't recode that to utilize the superior RLL 2,7 encoding scheme used
>by most (NON-IBM!) hard drives. RLL 2,7 typically gives an approximate
>150% storage space increase, presumably by using only 3 bits to encode
>2 input bits, instead of MFM's piggish 4 bits out for every 2 bits in.

Well, as you perhaps also read, there is already present the additional
feature of GCR (Group Code Recording) built into the system (into
hardware? Into Paula?). This is quasi the predecessor of RLL, putting
4 data bits into 5 written ones. (It is in use on Commodore floppies
from the first PET days until today in the C64 drives.) So this is even
more effective, theoretically. The caveat is that the Amiga hardware
(Paula?) can't read this reliably and must be cut down to half speed,
so effectively you gain only 4 bits out of 10. So finally MFM is more
effective and used for that reason.

I have no idea whether this could change with today's more advanced
technology. Also have no idea whether implementation of RLL would 
need new custom chip(s).

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