Is there a Catweasel like device for hard disks?

[Chuck Guzis]

> Date: Wed, 02 Jan 2008 14:28:23 -0600
> From: Jules Richardson <jules.richardson99 at gmail.com>

> Andrew Lynch wrote:
> > Hi,
> > Just out of curiosity, is there a technique or device which can do raw
> > reads of tracks on ST506/ST412 style hard disk drives similar to how a
> > Catweasel can with a floppy disk drive?
> 
> To the best of my knowledge, no - and I've been keeping an ear to the
> ground for such things for a while (plus it's a discussion which crops up
> here every once in a while, but I don't believe anyone's produced any
> working hardware yet).
> 
> The speeds involved (particularly if over-sampling the data) are
> reasonably high - enough that it'd be tricky[1] to throw something
> together out of OTS TTL parts. That puts such a project more within the
> realm of people who know all about interfacing to high speed
> microcontrollers, and the pool of available carbon units with the time,
> skills and inclination to make such a device is pretty darn small.

I'll assume that we're talking about (surviving--and that's a real 
gotcha) ST506/ST412 interface drives here.   Why would a Catweasel-
type interface (i.e. pulse time sampling) be even desirable?  All the 
drives used to store digital data that I'm aware of were recorded as 
MFM, M2FM or some flavor of RLL (2,7 probably being the most common). 
Controllers differ in small details such as address marks which 
renders them mutually incompatible, but the data stream has far less 
variation in encoding than the floppy world. 

Just give me a programmable data separator and a way to capture that 
output--I'll figure out what the bits mean.

The rated speeds of old ST412-type drives were pretty modest; about 
5MHz for MFM and 7.5MHz for RLL, IIRC.  

Cheers,
Chuck