You can erase a hardrive without destroying it (say you were selling it, or donating it). No software or computer erasure program can do it, however you can utterly obliterate any information or echos of information by erasing the drive with a magnetic bulk eraser, such as TV stations used to erase 1" and 2" reel to reel video tapes.
Originally Posted by copake_ham
EDIT-I have only used it on disposing of drives, now that I think of it, I wonder of the delicate parts of the mechanism would survive the magnetic field. It may be just a good way to destroy a drive