Hard disk drive

A hard disk drive (HDD; also hard drive, hard disk, or HD) is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the platters. Introduced by IBM in 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity.

Hard disk drives have been the dominant device for secondary storage of data in general purpose computers since the early 1960s. They have maintained this position because advances in their recording density have kept pace with the requirements for secondary storage. Today's HDDs operate on high-speed serial interfaces; i.e., serial ATA (SATA) or serial attached SCSI (SAS).

Starting with the introduction of the iPod shuffle in 2005, Apple began employing solid-state drives (SSDs) using flash memory instead of magnetic platters to reduce the size of their iPod music player line. This extended to their Mac product line with the introduction of the MacBook Air, which offered an optional SSD upgrade in place of a hard drive for high speed, low latency storage.