My dad worked for DEC in the 70's and 80's. When I was young he took us in and showed us a cabinet that had a bunch of spinning platters in it. They looked like 12" record albums, but they were light brown and made of metal. At least that's how I remember it, and I imagine they were the precursors to today's spinning hard disks.
My dad let my brother and I take a couple retired disks home. We tried to play frisbee once or twice with them, and then wisely decided that was probably a bad idea.