>I like the ideas about digitizing the stream of raw disk data.
>I imagine it would be possible to perform some software-based
>analysis and repair, rendering previously scrogged disks readable.
>Or perhaps the forensic-style recovery of erased data, reading
>and averaging adjacent off-center track information.
>
>I seem to remember a PDP guy on this list who recovers reel tape
>data this way, digitizing the raw tracks and processing with
>software, as opposed to relying on antique hardware methods for
>decoding the stream.
That would've been me, I think :-). It really is straightforward
to do today - a PC, a few hundred dollars of investment for the A/D hardware
and cabling, an old 9-track or 7-track drive that you can set up
to spool forward at a constant rate, and you've got the hardware side
done. The analysis software is where the real magic occurs - look up
"PRML" in a good engineering or math bookstore and you'll be on the right
path. Incorporating the data from non-flaky channels to recover the data
in the flaky channel is easy for 1/2" magtapes because of the existence
of both longitudinal and horizontal parity bits.
The same techniques work for 8", 5.25", and 3.5" floppies, too. You
don't have the luxury of parity channels there, but PRML techniques
put you way ahead of traditional data separators.
--
Tim Shoppa Email: shoppa_at_trailing-edge.com
Trailing Edge Technology WWW: http://www.trailing-edge.com/
7328 Bradley Blvd Voice: 301-767-5917
Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Thu Jun 01 2000 - 16:32:42 BST