Hard disk. View of a computer hard disk memory mechanism. This consists of a read/write head (metal arm) on a rigid hard disk coated on both sides with magnetic material. The direction of magnetization of small localised areas of the disk represents the stored information in binary digits. Information is written and accessed by means of small electromagnets in the read/write head. The disk rotates on a central spindle (at centre right) and the head moves radially to access different parts of the disk.