> On Tue, Dec 22, 1998 at 04:21:03AM -0500, Dave Cinege wrote:
> >
> > AFAIK DoD military grade wiping is zero->random->zero->random->zero.
>
> Actually, it's all-bits-zero, all-bits-one, all-bits-zero. This prevents
> people from reading the previous data from residual magnetic fields underneath
> a disk which has simply been wiped with zeroes, etc. The complete cycle for
> each bit is enough to minimize this risk.
No. DOD military grade wiping is a MRI then a sledge hammer :).
The all-bits method wont work right, as the drive uses fancy encoding
(like mfm). Writing all zeros doesn't zero the drive and even if it did
you could still read the off-angle magnetic bias. This is a complicated
issue and there are a number of good papers on it. Someone already posted
a good whiping program.
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