50% of the world's neodymium magnets are currently used in computer hard disc drives (HDDs), each of which typically contains two magnets. The magnets are used in actuators, a device that moves an actuator arm topped by a magnetic head that reads and writes data. Using magnets to drive the arms means that mechanical wear and tear is not an issue, unlike older stepper motor-driven hard disc drives.
The magnets used in hard disc drives are very strong neodymium (rare earth) magnets, hard disc drive magnets are different in that they act like two magnets glued side by side on one side with the North Pole on the left and the South Pole on the right, and on the other side with the South Pole on the left and the North Pole on the right, as shown in the diagram below.
Magnetization diagram of hard disk drive magnet;