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thoroughly debunked the myth ?
Authored by: Osc on Feb 05, '09 03:19:17PM
from :
[Further Epilogue]
"A recent article claims to be unable to recover any overwritten data using an MFM to perform an error-cancelling read. This isn't surprising, since the article confuses two totally unrelated techniques. One is the use of an MFM to recover offtrack data, discussed in paragraph 7 of section 2 and illustrated in one of the slides from the 1996 talk (and in several of the papers cited in the references). The other is the use of an error-cancelling read (in this case using a high-speed sampling scope) to recover overwritten data, discussed in paragraph 6 of section 2. Unfortunately the authors of the article confused the two, apparently attempting to perform the error-cancelling read using an MFM(!!) (I'm currently on holiday but will try and contact them when I get back to verify this... I wish they'd asked me before they put in all this effort because I could have told them before they started that this mixture almost certainly wouldn't work). Given that these are totally different techniques exploiting completely unrelated phenomena, it's not surprising that trying to use one to do the other didn't work."

Same page, further up:
"In the time since this paper was published, some people have treated the 35-pass overwrite technique described in it more as a kind of voodoo incantation to banish evil spirits than the result of a technical analysis of drive encoding techniques. As a result, they advocate applying the voodoo to PRML and EPRML drives even though it will have no more effect than a simple scrubbing with random data. In fact performing the full 35-pass overwrite is pointless for any drive since it targets a blend of scenarios involving all types of (normally-used) encoding technology, which covers everything back to 30+-year-old MFM methods (if you don't understand that statement, re-read the paper). If you're using a drive which uses encoding technology X, you only need to perform the passes specific to X, and you never need to perform all 35 passes. For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, "A good scrubbing with random data will do about as well as can be expected". This was true in 1996, and is still true now."

That said, I use what googoo/Mark suggests: srm =]

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thoroughly debunked the myth ?
Authored by: bdm on Feb 06, '09 10:53:08PM

I don't get your point. The article you link to is more than 10 years earlier that the one claiming to debunk it.

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thoroughly debunked the myth ?
Authored by: ghay on Feb 08, '09 06:55:42AM

That's because you haven't taken the time to read either.

The article "debunking" multiple overwrites, is completely flawed - as it says in the posters text. They use incompatible methods of reading and writing.

For the more hard of reading, it would be like storing English data in German, but then using a Spanish->English translator to read it back - the result - you can't read it.

That isn't "debunking" it's bad science.

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