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What is the universal (world wide) understanding behind degaussing harddisks?


On Mon, Apr 2, 2018 at 9:34 AM, Ken D'Ambrosio <ken at jots.org> wrote:

>
> 2) I dunno -- it was pretty damn long-winded, but seemed above-board.
> Me?  I've *never* seen convincing proof that anything could be recovered
> from a drive that's been completely overwritten once with *anything*.  I'm
> sure the DOD, etc., use crazy overwrite schemes, but the tolerances are
> already vanishingly small just to store the data, much less recover
> overwritten data.  Not saying it's impossible, but unless you're worried
> about the NSA, I'm thinking "one pass and done" is the answer.  Almost
> certainly preferable to actual degaussing, as that likely *would* leave
> remnant bits, unless you just completely overwhelm it.  Which is likely
> beyond the means of old degaussing rings used for fixing CRTs and the like.
>

If someone told me to "degauss" a hard drive, I would NOT suggest any
software to do it, because it's not technically possible. Degaussers
(attempt to) ELIMINATE residual magnetic fields. Hard drive heads CREATE
magnetic fields in tiny spots on the platters, and in fact the drive
DEPENDS upon the existence of magnetized regions to operate. Unless there's
a paranoid drive containing a built-in self-destruct feature, I believe it
is not possible tell a drive to remove ALL magnetic fields from the
platters, which is what a "degausser" would do.

In my (very limited) experience, one can use an "old fashioned" tape
"degausser" aka "demagnetizer" on a hard disk, but after doing so the drive
is generally "toast." (I suspect the head mechanism gets damaged by the
process, and the motors probably don't take kindly to being degaussed
either.) SO it would be impossible to determine whether residual data could
be retrieved from a degaussed drive without taking it apart and examining
the platters in the same manner as a data recovery service might do.

I suggest that a more time-efficient way to prevent access to information
on a hard drive is by putting it through a metal shredder.

For most purposes I would suggest a very strong magnet or degausser
followed by the judicious application of a drill or heavy hammer to the
platters might be sufficiently secure, but I am probably not paranoid
enough.

(As I write this I recall a storage shelf containing dozens of old drives
dating back decades that I haven't even taken the time to reformat.)
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