From: Jules Richardson <jules.richardson99 at
gmail.com>
Hmm, I thought I read once that you could throw
pretty much anything you
wanted at a ST506 drive so long as it was within the various tolerances -
is that not true of ST412-type drives?
While that may be true in theory, I'm going to guesstimate that 99
and 44/100 percent of the applications of the ST506/412 out there
used either MFM, MMFM (maybe) or 2,7 RLL for recording. While anyone
could throw together a bunch of TTL chips to record any old way on a
floppy (and did), implementing a hard disk controller with random
logic wasn't a simple matter and almost all manufacturers, by the
time of the ST506 used commodity solutions.
If by 'commodity solutions' you mean the WD1010 or whatever, then I have
to disagree with you. Plenty of manufactuers used their own ASICs in the
hard idsk controller, and admittedly most of them did do a fairly normal
MFM or RLL2,7 encoidng. But I'll bet at least one didn't!
And I've got machiens that use a 8x305 in the hard disk controller. And
of course the PERQs ahve a microcoded thing with a 2910 sequencer. It was
originally designed to talk to a SA4000, A kludgeoard was added (and the
CPU microcode device diivers changed) to talk to a Micropolis 1203, and
finally a different kludgeboard and CPU microcode were used to talk to
ST412 drives. I would not want to bet that the encoding on that was
normal, at least not without doing a lot of tests.
-tony