31 Oct
2008
31 Oct
'08
2:30 p.m.
I'm new here so I apologize for opening this old can of worms :-)
On Friday (10/31/2008 at 12:12PM -0500), Jules Richardson wrote:
Chuck Guzis wrote:
That's the path I've been on. I envision over-sampling and then just
playing and recording what was sent to the drive. I'd make no attempt
to go inside that datastream and try to interpret what was read or
written.
If entire tracks were always written, then it seems rather straightforward
to just store track images and play and record them as they are seeked
to.
It may not be that much harder to do the same on a sector basis. It's
just more critical timing of when you play back stuff or decide which
sector you are in when data comes at you with the write gate open.
I have considered using the SPI (or similar) interface on a
microcontroller to yield a parallel to serial/serial to parallel
conversion but that is about as far as I have thought about this...
other than reading the ST-506 manual that has been referenced elsewhere.
On 30 Oct 2008 at 17:44, Jules Richardson wrote:
Sure, but I believe one of the assumptions was that it'd be useful to
oversample the data and decode in software (possibly as an aid in error
recovery, possibly to make the hardware independent of data encoding used -
I don't remember which). I think the end of the last discussion on this
resulted in the conclusion
that it could be done, but required frequencies high enough to rule out
just slapping some TTL together on a bit of prototype board...
ISTR the bitrate from a ST412 drive was about 5 MHz, or one bit every 200
nsec/8 bits per 1.2 usec. That doesn't seem to be all that high to me--at
least not in terms of today's logic. I think I remember that RLL 2,7
drives had to be able to handle 7.5 MHz data. That ends up pushing things into tens of MHz, and I
suspect there's quite a
few people who can happily throw LS-TTL logic onto a bit of breadboard but
who don't have the experience or equipment to make something running at
that sort of speed.
We've got a lot of microcontroller options these days with most of that
highspeed stuff already on the device.
Perhaps I'm completely misremembering, though, and
mixing up a device which
can archive a drive from a device which emulates such a drive (and it's
only the emulation which needs the oversampling aspect)
Related note: I think there's a whole range of data recovery devices /
techniques that are worth thinking about (not only just with hard drives) -
I keep wondering if a separate discussion medium for such topics would be
useful, along with the support of various computer museums, but then we
know how people can't generally agree on anything when it comes to some of
these things :-) Seems a shame both that there's a wealth of info
scattered around out there that could in theory be collected together, and
that separate groups could easily end up doing the same tasks in parallel.
Ya... so, again I'm new here :-) But I'll go away quitely and think about
this some more-- knowing now that I can't cheat and do tracks at a time.
Thanks for the input in any case.
Chris
--
Chris Elmquist
mailto:chrise at pobox.com