There are several ways to destroy a hard drive. The only way to irrevocably destroy data is to destroy the platters. But there are other options available. Firstly, there is a data eraser called Darik's Boot and Nuke. It comes in Floppy or USB flash drives or it can run from CD/DVD. The only way to be certain that it is unrecoverable is to make sure the platters are unspinnable. Or you can
. put the platters between very strong magnets, set them on the circuit board for a couple of hours and it will wipe away all traces of data. You can drill four holes through the platters which will ensure that it never spins right again, however the data will still be on the drive. Or you can unscrew and remove the platters and scuff the surface of the platters until the shine is gone. Or, possibly take it to an industrial shredder where they can shred it. If you don't want to or don't have access to any of those, I recommend using a sledge hammer and totally destroying it, breaking it down in to itty bitty tiny pieces.
