A keyboard is a computer hardware input device. Originally based upon the design of the mechanical typewriter, computer keyboards have evolved with technological advances much as other computer hardware has evolved. New ergonomic keyboards can cost as much as a central processing unit or quality computer monitor. Besides the mouse, the keyboard is often the principal input device on home and office computers. Although primarily used for text input, keyboards are also used for precise image and interface manipulation, sending special commands to the operating system, and even controlling characters and objects in computer games. Some keyboards include other input/output features such as card readers, USB ports, or integrated trackballs. Although there are pseudo-standards regarding key arrangement, keyboard manufacturers are free to create original arrangements and designs. While most keyboards intended for use in English-language environments use the QWERTY layout, many keyboards are available with alternative layouts such as Dvorak. Some specialty keyboards have two or more layouts or languages printed on the keys, while others have no layout printed at all. These blank keyboards are intended for touch-typists only, who have no need to look at the keyboard while entering information.
Most conventional keyboards are built using dome-membrane technology. In these models, keys are mounted on a tray which affords them up and down movement only. The keys are supported in the up position by rubber membrane domes on which they rest. The domes are easily collapsible, and quickly return to their upright positions when released from the collapsing force. The underside of each dome houses a graphite bullet, which completes an open circuit underneath the dome when the dome is collapsed. Special circuitry senses the completed circuit, and translates this to a keypress which is then transmitted to the computer. Complex circuitry grids and patterns allow most keyboards to support over one hundred different keys with only about two dozen different circuits. In fact, careful layout of specific meta keys allows two- and even three- key-press combinations to be registered. More complex key-press combinations require very specialized circuitry, which few keyboards today support.
In addition to standard flat keyboard layouts where all alphanumeric keys are grouped together, as was the case in virtually all typewriters, recent ergonomic keyboard designs feature creative key placement and shape. These keyboards are designed to increase user comfort, typing speed, and to reduce common ailments associated with prolonged keyboard use such as carpal tunnel syndrome. Most popular among the ergonomic keyboards is the split design, in which keys pressed by the left hand are physically separated from those pressed by the right hand. As much as ten centimeters may separate the key groups, providing a more natural hand position than a single group of keys does. Some ergonomic keyboards go so far as to offer two completely separate boards that can be positioned independently of one another. Other innovative keyboard designs include chorded keyboards, hand keyers, and Kanji tablets. Chorded keyboards typically have between 5 and 12 keys, which are pressed together in order to form letters in a fasion akin to guitar chording. Chorded keyboards are usually intended for one-hand use. Similar to the chorded keyboard is the hand keyer. While the operation of a hand keyer is comparable a chorded keyboard in that multiple fingers are used simultaneously in order to type a single letter, hand keyers are worn on the hand or arm instead of lying on a table. This makes them more comfortable for some users, as well as affording a certain amount of mobility for portable devices such as PDAs. Kanji and other tablets, which have super-small keying surfaces capable of supporting hundreds of characters in a reasonable amount of space, are designed for use with languages which have too many characters to assign an individual key on a conventional keyboard. This is typical of many Asian languages. Kanji tablets are now considered outdated, as more efficient text input systems have been designed which allow Asian character input on conventional-style keyboards. Keyboards designed for use with these systems have an additional 5 keys dedicated to interface with specialty character input software.
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