1 Jan
2002
1 Jan
'02
1:51 a.m.
see below, plz.
Dick
----- Original Message -----
From: "John Foust" <jfoust(a)threedee.com
To: <classiccmp(a)classiccmp.org
Sent: Tuesday, January 01, 2002 7:13 AM
Subject: Re: Compaticard (was: Any AMIGA users?
The Amiga did the MFM decoding using software and its
custom chip - the blitter, I believe, which could perform
somewhat complex logical operations. They no doubt did this
to save on hardware, like Woz's disk controller.
The specific hardware required to do the RLL would have been an 'LS299 shift
register, and little else. I expect the choice was made because it was
considered adequate and considerably easier to use an essentially
hard-sectored (single-sectored) scheme than to introduce the overhead, and
resulting loss in capacity, imposed by multiple sectors. The early
Tallgrass Technologies controllers, e.g. the one for S-100 used that
strategy together with GCR. Once you decide to use a single sector and sort
it out in software, the modulation scheme is quite arbitrary.
At 10:11 PM 12/31/2001 +0000, Richard Erlacher wrote:
please note that I didn't write this, since I'm quite ignorant of AMIGA
matters.
>> The Amiga IS MFM! But it does not have WD
style sector headers.
>> It reads and writes a track at a time, and parses it in software.
There
are no gaps, synchronization issues between sectors,
etc.
That's almost enough to make one wonder why they used MFM. Had they used
RLL, which requires no complicated, or even simple modulator, they'd have
had half-again the capacity.