[clug] Re: More (almost free) stuff. - 3.5" WD 200GB IDE - $10

Ian darkstarsword at gmail.com
Sun Sep 7 10:33:39 GMT 2008

I have heard a technique described to recover data from an overwritten
drive - no idea whether it would actually work or not though.

The idea is that you would hook up some sort of digital oscilloscope
directly to the read head to be able to observe the magnetic pattern
on the disk as the head reads it and compare that to what the drive
tells you is in that location. You build up a profile of what a 1
generally looks like by taking the profile of every individual 1 on
the disk and averaging them together, do the same for every 0. Then
you go through and for every bit on the disk you subtract the average
profile from the individual profile. This will leave you with a new
much more subtle profile left over from whatever data was in that
location on the disk previously. Repeat the process however many times
the disk was overwritten - as you can imagine the recoverability of
the data would be dependant on the sensitivity of the head &
oscilloscope and how many times the data has been overwritten since
the left over profile will be harder to detect for each overwrite.
More overwrites will require more expensive equipment to recover the
data with.

So, anyone have any idea whether that's even plausible or not?


On the day *I* go to work for Microsoft, faint oinking sounds will be
heard from far overhead, the moon will not merely turn blue but
develop polkadots, and hell will freeze over so solid the brimstone
will go superconductive.
 -- Erik Raymond, 2005
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