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. First announced by IBM on September 14, 1956, hard disk drives have decreased in cost and physical size over the years while dramatically increasing in capacity.

History
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).

Adoption by Apple
The first hard drive to be offered by Apple Computer was the ProFile, released for the Apple III in September 1981. This external drive contained a 5 MB mechanism that offered more storage space and speed than floppy drives. The ProFile also supported the Apple II and Lisa series computers.

The first external hard drive sold by Apple for early compact Macs was the Hard Disk 20. Though it offered more space than 400 KB floppy disks used at the time, its maximum throughput was hampered by its reliance on being connected through the floppy drive connector. The first Macs to be designed to accommodate an internal hard drive were the Macintosh SE and II, released in March and April 1987, respectively. These utilized a dedicated internal SCSI port for greater maximum throughput. Starting with the Macintosh Quadra 630 in July 1994, Apple transitioned from using SCSI to the more widely-used IDE interface for internal hard drives. With the introduction of the Power Mac G5 in June 2003, Apple then began using the faster SATA interface for internal hard drives.

Transition to solid-state drives
With the release of the 1st-generation iPod shuffle in January 2005, Apple began employing solid-state drives (SSDs) using flash memory instead of the magnetic platters of hard drives to reduce the size of their iPod music player line. This extended to their Mac product line in January 2008 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. With the introduction of the M1-based 2021 iMac, Apple no longer offered hard drives (or hybrid drives) of any kind as a factory option in their current product lineup.