Re: Linux FS Question
On Wed, 18 Jun 1997, Christian Hudon wrote:
> On Jun 18, Rick Macdonald wrote
> >
> > Well, you could overwrite the file with gibberish _before_ deleting it.
> > I think that's what Norton does, several times if I remember correctly.
> > That's to comply with US federal regs, which seem a bit superstitious to
> > me! Actually, the giberrish itself is probably some specified bit pattern.
>
> Actually it's not superstition at all. I think you can still recover a file
> that's been overwritten once with zeroes... just open the HD (in a clean
> room, of course) and read off the sectors with a electron microscope (or
> something like that). The voltage levels will all be bellow the 'zero
> threshold' but they won't be all equal, and from the small variations you
> can recover the contents of the file before it was overwritten with
> zeroes. Of course, whatever was written on your hard drive must be worth
> quite a bit of cash (to you or to other people) for this recovery method to
> make sense economically. So the 'overwrite multiple times' precaution is
> probably overkill for the vast majority of people.
I used to recover some badly trashed floppys under M$DO$ with Central
Point Software PCFormat (CPS has been absorbed by Symantic/Norton).
Somehow it could read and rewrite every byte on the disk. Saved some
peoples hyde down at the old rubber factory. That tells me that it
may be quite possible to read an overwritten disk. But multiple
overwrites with varying patterns should make that impossible.
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