Is there a Catweasel like device for hard disks?

Chuck Guzis cclist at
Thu Jan 3 10:55:15 CST 2008

> From: Jules Richardson <jules.richardson99 at>

> 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.

That's not to say that there aren't any bizarre recording schemes out 
there for ST506s; just that I've never run into one.  

For example, I've got a few mutually incompatible 2,7 RLL PC-AT style 
controllers, but they differ more in logical details (address marks, 
header layout, ECC codes) than they do in modulation methods or clock 
rate.  While it may have been possible to, say, employ FM recording 
on a ST412, I've never seen it done in practice.   There *were* some 
RLL variants that attempted to push things past 2,7 (Perstor?) on a 
412 interface, but they were never very reliable or popular.

Did any application of a 506 even use zoned recording (i.e. using a 
faster data clock on the outer cylinders)?


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