Circuitry of hard disk drive taken from a PC, 1998.

Computers require a data storage medium to contain the input and output data from the computer as well as the program to be performed by the computer. Modern computers contain hard drives - sealed units containing one or more hard disk. Hard disks hold more information than floppy disks and provide faster acces to data. Today's computers come equipped with a hard disk containing several billion bytes (or gigabytes) of storage.