A direct-access storage device (DASD) is a secondary storage device in which "each physical record has a discrete location and a unique address". IBM coined the term DASD as a shorthand describing hard disk drives, magnetic drums, and data cells. Later, optical disc drives and flash memory units are also classified as DASD. The term DASD contrasts with sequential storage media such as magnetic tape, and unit record equipment such as card devices like card readers and punches.
