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

On Mon, Apr 02, 2018 at 11:23:29AM -0500, John Hasler wrote:
The equipment required for degaussing isn't very special (though it
*does* require an AC magnet).

You need to match the strength of the equipment to the media in use. Modern hard disks need fairly strong fields to fully erase, and there's a lot of older equipment out there which simply won't work well because it was designed to erase older media.

However, a determined opponent can
probably recover data from a degaussed disk.

Not one that's properly degaussed. But, as I said, verification is difficult.

Overwriting with zeros is
probably more effective with modern disks (the hard part may be making
sure every physical sector actually does get overwritten).

Overwriting with zeros is sufficient and effective for most purposes. The erase 7 times with patterns stuff is basically techie mumbo-jumbo. It can leave traces in non-writable parts of the disk, which the secure-erase commands attempt to address. The main reasons to look at degaussing or other methods of destruction are 1) for extremely sensitive data, 2) for drives which are broken (it's quite possible for something to be too broken to overwrite, but not too broken to extract data) or 3) because it's quicker/easier/cheaper to destroy a bunch of hard disks than to erase *and verify*.

Mike Stone