[no subject]

The "ghosts" are called "fringe effects".  Ones and Zeros on a disk
have physical dimension and I assume the strength of the magnetism
fails off in a gausian curve (Think back to advanced physics class). 
Head alignment is not perfect, so over-writes do not exactly
over-write, but instead the center of the curve is slightly offset. 
As you say a highly calibrated and sensitive head assembly can in
theory read the field strength of the magnetism with a far greater
accuracy than just 1/0.

Then very complex software can "in theory" reassemble the underlying data.

I am not aware of any commercial provider offering that they can read
"fringe effects".

I'd be very interested to know of a commercial service provider that
can actually do that.

I've heard the rumors that CIA / NSA / etc. can do this and I have
little reason to doubt it, but I imagine they can only get little
fragments of data, not full recovery.

FYI: The biggest support for this capability existing is the DOD
wiping requirement that requires multiple passes.  If technology does
not exist to read data after a single over-write, then the DOD
requirement is overly strict.

Greg


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