The magnets used in hard disk drives are very strong neodymium (rare earth) magnets. Typically a magnet will have a north pole on one face, and a south pole on the other face. Hard drive magnets differ in that they act like two magnets stuck together side by side. On one face there is a north pole on the left and a south pole on the right, on the other face there is a south pole on the left and a north pole on the right....