Path: utzoo!utgpu!watserv1!watdragon!lion!ccplumb
From: ccplumb@lion.waterloo.edu (Colin Plumb)
Newsgroups: comp.sys.amiga.tech
Subject: Re: How does the blitter decode/encode MFM data?
Message-ID: <20446@watdragon.waterloo.edu>
Date: 2 Feb 90 01:50:02 GMT
References: <75676@tut.cis.ohio-state.edu> <242@sunee.waterloo.edu>
Sender: daemon@watdragon.waterloo.edu
Reply-To: ccplumb@lion.waterloo.edu (Colin Plumb)
Organization: U. of Waterloo, Ontario
Lines: 18

In article <242@sunee.waterloo.edu> sjorr@sunee.waterloo.edu (Stephen_Orr) writes:
>An article on this very topic (and the source of my knowledge) was written
>by Betty Clay, and appears in V3 I1 of the Amiga Transactor.

It is also wrong in a couple of points, most notably in asserting that
GCR, due to its 4/5 data rate, achieves greater density than MFM's 1/2
rate.  It does not point out the need for the two differnt bit clock
rates (2us and 4us) due to the different minimum run lengths in the
codes.  Since it's safe to clock out MFM at twice the rate, it gets
20% more bits in the same amount of disk space.

The interaction of encoding schemes and analog channel design
(everything that talks to the read/write head) is a complex one.  See
Magnetic Recording (especially volume II, computer data storage) by C.
Denis Mee and Eric D. Daniel for all the details.  This three-volume
set has more than you ever really wanted to know on the subject.
-- 
	-Colin