Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!nrl-cmf!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!unido!tub!tmpmbx!netmbx!hase
From: hase@netmbx.UUCP (Hartmut Semken)
Newsgroups: comp.sys.atari.st
Subject: Re: What are MFM and RLL drives and which should I get?
Message-ID: <2087@netmbx.UUCP>
Date: 31 Jan 89 20:51:10 GMT
References: <6102@saturn.ucsc.edu>
Reply-To: hase@netmbx.UUCP (Hartmut Semken)
Organization: netmbx Public Access Unix, Berlin, West Germany
Lines: 39

In article <6102@saturn.ucsc.edu> humtech@ucschu.ucsc.edu (Mark Frost) writes:
>
>I've seen talk recently about formatting MFM drives using RLL neither of which
>I've ever heard of. I take it that they are some sort of hard disk formatting
>techniques or types of hard disks.

MFM and RLL (modified frequency modulation and run lenght limited) are
methods to encode data (bytes) to be stored on media.

They define a timing of the serial signal send to the hard disk (or
received ...).


The information is packed a little denser using RLL. Some (older) MFM
drives cannot take the higher density. 
To put more information in the same place, RLL encoding uses less space
for "clock" and similiar signals. That - and the increased density -
squeeze some more capacity out of the same drive; 50% with RLL, 90% with
ARLL (advanced RLL).


Some people say, formatting an non-RLL drive with an RLL controller,
voids the warranty.
This is true for some drives: their media could take the higher density,
but their electronic must no be used with signals, seldom returning to
low level (line drivers blow up...).

Most new drives can be used with RLL. If formatting with RLL does not
work (media not capable ...), the drive isn't hurt and will run with any
MFM controller.

I prefer ARLL over MFM: it gives me twice the capacity and 2.5 times the
speed...

hase
-- 
Hartmut Semken, Lupsteiner Weg 67, 1000 Berlin 37 hase@netmbx.UUCP
If there is something more important than my Ego, I want it caught and shot.
Now! (Zaphod Beeblebrox)