A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive, is a non-volatile storage device which stores digitally encoded data on rapidly rotating platters with magnetic surfaces. Strictly speaking, "drive" refers to a device distinct from its medium, such as a tape drive and its tape, or a floppy disk drive and its floppy disk. Early HDDs had removable media; however, an HDD today is typically a sealed unit (except for a filtered vent hole to equalize air pressure) with fixed media.
HDDs (introduced in 1956 as data storage for an IBM accounting computerwere originally developed for use with general purpose computers. In the 21st century, applications for HDDs have expanded to include digital video recorders, digital audio players, personal digital assistants, digital cameras and video game consoles. In 2005 the first mobile phones to include HDDs were introduced by Samsung and Nokia. The need for large-scale, reliable storage, independent of a particular device, led to the introduction of embedded systems such as RAID arrays, network attached storage (NAS) systems and storage area network (SAN) systems that provide efficient and reliable access to large volumes of data.
| Form factor | Width | Largest capacity | Platters (Max) |
|---|---|---|---|
| 5.25″ FH | 146 mm | 47 GB[13] (1998) | 14 |
| 5.25″ HH | 146 mm | 19.3 GB[14] (1998) | 4 |
| 3.5″ | 102 mm | 1.5 TB[6] (2008) | 5 |
| 2.5″ | 69.9 mm | 500 GB[16] (2008) | 3 |
| 1.8″ (CE-ATA/ZIF) | 54 mm | 250 GB[17] (2008) | 3 |
| 1.3″ | 43 mm | 40 GB[18] (2007) | 1 |
| 1″ (CFII/ZIF/IDE-Flex) | 42 mm | 20 GB (2006) | 1 |
| 0.85″ | 24 mm | 8 GB[19] (2004) | 1 |
IDE interface (PATA)
SATA Interface
