7 Jan
2016
7 Jan
'16
9:36 a.m.
> 1) if the alignment of the head of the original
recording and of the
> overwrite head are not a perfect match, then there can be some residual
> data somewhat off axis.
On Thu, 7 Jan 2016, Christian Corti wrote:
At a first thought I don't see how there can be
residual data because there
is the tunnel erase head after the R/W head. The drives must be very
misaligned (i.e. more than the width of one erase half) to still have
residual data.
Yes, that makes sense. But, the erase head probably doesn't scramble the
weak residual flux transitions as much as overwriting does.
2) if the data
was overwritten once, with a known pattern, then somebody
with sufficient resources and motivation can attempt to analyze the noise,
and determine "what, overwritten by a 0 could produce the noise that we
have here." Accordingly, there are guvmint standards of MULTIPLE patterns
to
That is why you don't take /dev/zero but /dev/[u]random for overwriting
data.