Magnetic+Hard+Disk

IBM developed magnetic disk drives in the late 1950s. The disk drive allows rapid random access to large armount of data. All disk drives use a thin circular platter made of non-ferrous metal or plastic and rotate it at up to 10,000 revolutions per minute beneath a read-write head that moves radially across the surface of the platter. The platter is coated with an emulsion of iron or cobalt oxide particles that act as tiny magnets. Binary data is recorded by aligning these tiny magnets in one direction to represent a binary 0 and in the opposite direction to represent a binary 1. Binary data is recorded in concentric rings, or tracks, subdivided into sectors that hold a fixed number of bytes, such as 512. A hard disk can store and retrieve a large volume of data.

The highest capacity for a Magnetic Hard Disk is 3 TB (As of July 2010)