31 Oct
2008
31 Oct
'08
10:12 a.m.
Chuck Guzis wrote:
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).
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.
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.
cheers
Jules
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.