External Hard Disk Drive Views
A hard disk drive[2] (HDD) is a non-volatile, random access device for digital data. 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 fallen 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.[3] They have maintained this position because advances in their areal recording density have kept pace with the requirements for secondary storage.[3] Today's HDDs operate on high-speed serial interfaces; i.e., serial ATA (SATA) or serial attached SCSI (SAS).
Not all the space on a hard drive is available for user files. The operating system file system uses some of the disk space to organize files on the disk, recording their file names and the sequence of disk areas that represent the file. Examples of data structures stored on disk to retrieve files include the MS DOS file allocation table (FAT), and UNIX inodes, as well as other operating system data structures. This file system overhead is usually less than 1% on drives larger than 100 MB.
Mainframe and minicomputer hard disks were of widely varying dimensions, typically in free standing cabinets the size of washing machines (e.g. HP 7935 and DEC RP06 Disk Drives) or designed so that dimensions enabled placement in a 19 rack (e.g. Diablo Model 31). In 1962, IBM introduced its model 1311 disk, which used 14l inch (nominal size) platters. This became a standard size for mainframe and minicomputer drives for many years,[28] but such large platters were never used with microprocessor-based systems.
External Hard Disk Drive Images
