Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!wuarchive!kuhub.cc.ukans.edu!jli
From: JLI@kuhub.cc.ukans.edu
Newsgroups: comp.sys.ibm.pc
Subject: Re: RLL controllers with MFM drives
Message-ID: <15668@kuhub.cc.ukans.edu>
Date: 26 Oct 89 01:34:34 GMT
References: <none> <2546@bingvaxu.cc.binghamton.edu> <4265@ncsuvx.ncsu.edu> <35883@srcsip.UUCP> <4273@ncsuvx.ncsu.edu>
Organization: University of Kansas Academic Computing Services
Lines: 42

In article <4273@ncsuvx.ncsu.edu>, unkydave@shumv1.uucp (David Bank) writes:
> 
>        Contrary to your assertion, plated media is NOT the sole
> basic difference in RLL-rated drives. The biggest single difference
> is in the use of VOICE COIL technology in the armature control
> mechanism. This is what allows the mush more closely controlled
> head movement demanded by RLL. The plated media simply makes
> for a more reliable rusty pie plate.
> 
>        Sure, I know people running MFM drives on RLL too. Its
> like the car you drive off the lot and it never needs to see a
> mechanic. Some RLL drives are just able to do it. You may be running
> them at the edge of tolerance, but you are just on this side of
> their operational capacity. I never meant to say it was IMPOSSIBLE
> to run an MFM drive on RLL. Merely dangerous with your data.
> 
>         No, not a blanket statement at all. As I recall, I
> qualified it with "probably".
> 
>         Oops. Two paragraphs back, 3rd line, "RLL" should be "MFM"
> These remote connections are hell on editing.
> 
> Unky Dave
> unkydave@shumv1.ncsu.edu

  This is NOT a flame, but I don't think the RLL-rated drives differ
from the MFM-rated ones based on the use of voice coil technology.
I am not sure how they related, but as far as I know, there are many
RLL-rated drives still using stepper motor to move the heads (such
as Miniscribe 8225, 8450, 8438, etc.) and MFM-rated drives using the
voice coil (such as Seagate 251-1, 4096, etc.).  I haven't done much
research (at least not enough) on hard drives and their specifications,
but I failed to see how one can differetiate RLL and MFM rated drives
based on the use of voice coil.

  By the way, I only see one person mentioned the different encoding
schemes that RLL and MFM systems (the encoding is done on the controller,
I think.) using, which should be the main difference between these two
types of systems.  In order to meet the RLL specification, a drive
has to have better physical characteristics and media quality.

M.C. Baldwin