Compaticard (was: Any AMIGA users?

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Jan 1 09:51:37 2002

see below, plz.

Dick

----- Original Message -----
From: "John Foust" <jfoust_at_threedee.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, January 01, 2002 7:13 AM
Subject: Re: Compaticard (was: Any AMIGA users?


> 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.
>
> 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.
>
Received on Tue Jan 01 2002 - 09:51:37 GMT