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

On Tue, Apr 3, 2018 at 11:06 AM, Tommy Trussell <tommy.trussell at gmail.com>

> 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.)
Drive shredders can be rented on the cheap. If you aim to ensure that there
is no chance that someone will read your old data when getting rid of a
drive, physical destruction is really the only option. Secure wipes are ok
for anything not mission critical, but anything that is mission critical or
contains intellectual property that you should protect, I always suggest
using a drive shredder.

Of course, if you're a home user with no such considerations, a single pass
wipe or even just a plain old reformat is likely good enough.
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