Hard disk

Hard disk drive

A hard disk drive (HDD), commonly referred to as a hard drive, hard disk, or fixed disk drive,^[1] 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.^[2]

Originally, the term "hard" was temporary slang, substituting "hard" for "rigid", before these drives had an established and universally-agreed-upon name. A HDD is a rigid-disk drive although it is rarely referred to as such. By way of comparison, a floppy drive (more formally, a diskette drive) has a disc that is flexible. Some time ago, IBM's internal company term for a HDD was "file".

HDDs (introduced in 1956 as data storage for an IBM accounting computer^[3]) were originally developed for use with general purpose computers; see History of hard disk drives.

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 configurations 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. Note that although not immediately recognizable as a computer, all the aforementioned applications are actually embedded computing devices of some sort.

Capacity and access speed

Using rigid disks and sealing the unit allows much tighter tolerances than in a floppy disk drive. Consequently, hard disk drives can store much more data than floppy disk drives and can access and transmit it faster. As of January 2008:

• A typical desktop HDD, might store between 120 and 1000 GB of data (based on US market data^[5]), rotate at 5,400 to 10,000 rpm and have a media transfer rate of 1 Gbit/s or higher^{[citation needed]}. (1 GB = 10⁹ B; 1 Gbit/s = 10⁹ bit/s)
• As of July 2008^[update], the highest capacity HDDs are 1.5 TB^[6].
• The fastest “enterprise” HDDs spin at 10,000 or 15,000 rpm, and can achieve sequential media transfer speeds above 1.6 Gbit/s.^[7] and a sustained transfer rate up to 125 MBytes/second.^[7] Drives running at 10,000 or 15,000 rpm use smaller platters because of air drag and therefore generally have lower capacity than the highest capacity desktop drives. Gamers may choose to get 10000 rpm Hard Drives for Gaming PCs due to the fast transfer rate substantially decreasing game load times (and startup times).^{[citation needed]}
• Mobile, i.e., laptop HDDs, which are physically smaller than their desktop and enterprise counterparts, tend to be slower and have less capacity. A typical mobile HDD spins at 5,400 rpm, with 7,200 rpm models available for a slight price premium. Because of the smaller disks, mobile HDDs generally have lower capacity than the highest capacity desktop drives.