Portable Hard Drives
A hard disk drive (HDD) is a data storage device used for storing and retrieving digital information using rapidly rotating discs (platters) coated with magnetic material. An HDD retains its data even when powered off. Data is read in a random-access manner, meaning individual blocks of data can be stored or retrieved in any order rather than just sequentially. An HDD consists of one or more rigid ("hard") rapidly rotating discs (platters) with magnetic heads arranged on a moving actuator arm to read and write data to the surfaces.
Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and PCs. More than 200 companies have produced HDD units, though most current units are manufactured by Seagate, Toshiba and Western Digital. Worldwide revenues for HDDs shipments are expected to reach $33 billion in 2013, down about 12% from $37.8 billion in 2012.
The primary characteristics of an HDD are its capacity and performance. Capacity is specified in unit prefixes corresponding to powers of 1000: a 1-terabyte (TB) drive has a capacity of 1,000 gigabytes (GB; where 1 gigabyte = 1 billion bytes). Typically, some of an HDD's capacity is unavailable to the user due to use by the file system and the computer operating system, and possibly inbuilt redundancy for error correction and recovery. Performance is specified by the time to move the heads to a file (Average Access Time) plus the time it takes for the file to move under its head (average latency, a function of the physical rotational speed in revolutions per minute) and the speed at which the file is transmitted (data rate).
The two most common form factors for modern HDDs are 3.5-inch in desktop computers and 2.5-inch in laptops. HDDs are connected to systems by standard interface cables such as SATA (Serial ATA), USB or SAS (Serial attached SCSI) cables.
As of 2012, the primary competing technology for secondary storage is flash memory in the form of solid-state drives (SSDs). HDDs are expected to remain the dominant medium for secondary storage due to predicted continuing advantages in recording capacity and price per unit of storage; but SSDs are replacing HDDs where speed, power consumption and durability are more important considerations than price and capacity.
Read more about Portable Hard Drives: History, Capacity, Form Factors, Access and Interfaces, Integrity and Failure, External Removable Drives, Market Segments, Manufacturers and Sales, Icons, See Also
Famous quotes containing the words portable, hard and/or drives:
““Wotever is, is right, as the young nobleman sveetly remarked wen they put him down in the pension list ‘cos his mother’s uncle’s vife’s grandfather vunce lit the king’s pipe vith a portable tinder-box.””
—Charles Dickens (1812–1870)
“I know this, and I know it from actual experience in the Orient, that the progress of modern Christian civilization has largely depended on the earnest hard work of the Christian missions of every denomination.”
—William Howard Taft (1857–1930)
“The one prudence in life is concentration; the one evil is dissipation: and it makes no difference whether our dissipations are coarse or fine; property and its cares, friends and a social habit, or politics, or music, or feasting. Everything is good which takes away one plaything and delusion more, and drives us home to add one stroke of faithful work.”
—Ralph Waldo Emerson (1803–1882)