Hard disk drive

Hard disk drive

A hard disk drive(hard disk,hard drive HDD) is a non-volatile storage device for digital data. It features one or more rotating rigid platters on a motor-driven spindle within a metal case. Data is encoded magnetically by read/write heads that float on a cushion of air above the platters.
Hard disk manufacturers quote disk capacity in SI-standard powers of 1000, wherein a terabyte is 1000 gigabytes and a gigabyte is 1000 megabytes. With file systems that measure capacity in powers of 1024, available space appears somewhat less than advertised capacity.
The first HDD was invented by IBM in 1956. They have fallen in cost and physical size over the years while dramatically increasing 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 areal recording density have kept pace with the requirements for secondary storage . Form factors have also evolved over time from large standalone boxes to today's desktop systems mainly with standardized 3.5" form factor drives, and mobile systems mainly using 2.5" drives. Today's HDDs operate on high-speed serial interfaces, i.e., Serial ATA (SATA) or Serial attached SCSI (SAS).
The presentation of an HDD to its host is determined by its controller. This may differ substantially from the drive's native interface particularly in mainframes or servers.
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