Chuck Guzis wrote:
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.
Indeed - I sorted through my pile of 'reserves' recently and got around a 2/3
mortality rate. On the flipside, it's been a while since I've had a working
drive suddenly fail on me - as though long periods of disuse are real killers
(perhaps things like seized spindles and heads sticking to platters, rather
than logic or head faults).
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).
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?
Although I suspect things fall into the same category as for a floppy reader -
the choices boil down to either oversampling the data in order to capture bit
transitions, or to recording the time between bit transitions (as I believe
the catweasel does).
The rated speeds of old ST412-type drives were pretty
modest; about
5MHz for MFM and 7.5MHz for RLL, IIRC.
Yep... I was thinking an 8x sampling rate would probably suffice, but with a
7.5MHz raw data rate that's probably a bit much for standard TLL ICs.
Recording the elapsed time between bit transitions might be better, though
(providing it's still possible to record the worst-case scenarios)
cheers
Jules