25 years ago when we had to destroy 5.25" full height 32MB SCSI drives (ha, ha, ha!), we'd zero them several times, then open 'em up and run the platters through Captain Crunch, the industrial shredder/grinder. A pile of chips, each about the size of a grain of rice, came out the other end.
This was in the Navy at an acoustic analysis center.
This was in the Navy at an acoustic analysis center.