The computer hard disk is usually used in tandem with the floppy disk. The hard disk drive offers much greater storage capacity and data access speeds than the floppy disk. The average data capacity of a single floppy disk is around 1 megabyte (1,000,000 bytes) of information. Hard disks, on the other hand, are available in capacities of up to 1.2 gigabits (1,200,000,000 bytes).
The hard disk is so called because the storage disks are made of a rigid magnetic material. These are non-removable and stored in a metal outer case. In most drives there are multiple disks with multiple read/write heads to service them. These heads float a microscopic distance above the disk's surface, polarising disk particles in the case of a write, and sensing magnetic particle polarity in the case of a read.
Computer information is stored on the hard disk as a series of binary digits (BIT's) which may have a 0 or a 1 state. These states are reflected by the direction of magnetic alignment, or polarity, of the disk particles.
In recent years hard disks have been miniaturised and made more robust to accommodate the growing lap top computer market.
