You can’t use your disk-based iPod (or laptop, or anything else with a mechanical drive for that matter) above ~10,000 feet because the air gets to be too thin. The reason that happens is that when the drive spins, the head is actually floating on a thin layer of air above the platters, and so when you get to too high of an altitude, the air is no longer thick enough to maintain that distance, and the head physically crashes into the platter of the device, resulting in disk failure (ie it won’t work even if you come back down).
So don’t go hiking with your iPod classic.