Floppy recovery

Fred Cisin cisin at xenosoft.com
Tue Jan 5 17:00:01 CST 2016

On Tue, 5 Jan 2016, ethan at 757.org wrote:
> If a disk has all zeros written to it, as far as I know from what I've read 
> there is no hope of recovering the data. There were rumors that the 
> government could do it based on really fine detection of magnetic levels or 
> something -- but it was rumor. There are bounties out there if anyone can 
> pull it off.

I will heartily agree that recovery ceases to be PRACTICAL.

NSA has done substantial serious research on that and other recovery.
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.
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 overwrite with to render such extreme techniques unusable.

However, I will heartily agree that recovery ceases to be PRACTICAL.

> I understand data can be recovered when the file entry is removed from an 
> allocation table but data has not been zereod/randomly written over.

truly trivial.

> tl;dr: single pass is fine -- no need to triple pass erase.

THAT depends on who is after you.   I don't do anything interesting enough 
to warrant using a simplistic trivial UNERASE utility.  (Which is what 
launched Norton fUtilities)
NSA is not interested in what I am doing.

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