Floppy recovery

[Christian Corti]

On Tue, 5 Jan 2016, Fred Cisin wrote:
> 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.

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.

> 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.

Christian