In
computing, a
keyboard is an
input device, partially modeled after the
typewriter keyboard, which uses an arrangement of buttons or
keys, to act as mechanical levers or electronic switches. After punch cards and paper tape, interaction via teletype-style keyboards became the main input device for computers.
Despite the development of alternative input devices, such as the mouse (computing mouse), touch sensitive screens, pen devices, character recognition, voice recognition, and improvements in computer speed and memory size, the keyboard remains the most commonly used and most versatile device used for direct (human) input into computers.
A keyboard typically has characters
engraved or
printed on the keys and each press of a key typically corresponds to a single written
symbol. However, to produce some symbols requires pressing and holding several keys simultaneously or in sequence. While most keyboard keys produce
letters,
numbers or
signs (
characters), other keys or simultaneous key presses can produce actions or computer commands.
In normal usage, the keyboard is used to type text and numbers into a
word processor,
text editor or other program. In a modern computer, the interpretation of key presses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all key presses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as
Windows'
Control-Alt-Delete combination, which brings up a task window or shuts down the machine.
Laptop-size
Keyboards on
laptops and
notebook computers usually have a shorter travel distance for the keystroke and a reduced set of keys. They may not have a numerical keypad, and the function keys may be placed in locations that differ from their placement on a standard, full-sized keyboard.
Thumb-sized
Smaller keyboards have been introduced for laptops, PDAs, cellphones or users who have a limited workspace. The size of a standard keyboard is dictated by the practical consideration that the keys must be large enough to be easily pressed by fingers. To reduce the size of the keyboard, the numeric keyboard to the right of the alphabetic keyboard can be removed, or the size of the keys can be reduced, which makes it harder to enter text.
Another way to reduce the size of the keyboard is to reduce the number of keys and use
chording keyer, i.e. pressing several keys simultaneously. For example, the
GKOS keyboard has been designed for small wireless devices. Other two-handed alternatives more akin to a
game controller, such as the
AlphaGrip, are also used as a way to input data and text. Another way to reduce the size of a keyboard is to use smaller buttons and pack them closer together. Such keyboards, often called a "
thumbboard" (thumbing) are used in some
personal digital assistants such as the
Palm Treo and
BlackBerry and some
Ultra-Mobile PCs such as the
OQO.
Numeric
Numeric keyboards contain only numbers, mathematical symbols for addition, subtraction, multiplication, and division, a decimal point, and several function keys (e.g. End, Delete, etc.). They are often used to facilitate data entry with smaller keyboard-equipped laptops or with smaller keyboards that do not have a numeric keypad. A laptop does sometimes have a numeric pad, but not all the time. These keys are also known as, collectively, a numeric pad, numeric keys, or a numeric keypad, and it can consist of the following types of keys:
- arithmetic operators such as +, -, *, /
- numeric digits 0-9
- cursor arrow keys
- navigation keys such as Home, End, PgUp, PgDown, etc.
- Num Lock button, used to enable or disable the numeric pad
- enter key
Non-standard or special-use types
Chorded
While other keyboards generally associate one action with each key,
chorded keyboards associate actions with combinations of key presses. Since there are many combinations available, chorded keyboards can effectively produce more actions on a board with fewer keys. Court reporters'
stenotype machines use chorded keyboards to enable them to enter text much faster by typing a syllable with each stroke instead of one letter at a time. The fastest typists (as of 2007) use a stenograph, a kind of chorded keyboard used by most court reporters and closed-caption reporters. Some chorded keyboards are also made for use in situations where fewer keys are preferable, such as on devices that can be used with only one hand, and on small mobile devices that don't have room for larger keyboards. Chorded keyboards are less desirable in many cases because it usually takes practice and memorization of the combinations to become proficient.
Software
Software keyboards or On-Screen Keyboards often take the form of computer programs that display an image of a keyboard on the screen. Another input device such as a mouse or a touchscreen can be used to each virtual key to enter text. Software keyboards have become very popular in touchscreen enabled cell phones, due to the additional cost and space requirements of other types of hardware keyboards. Microsoft Windows and Mac OS X both include on-screen keyboards that can be controlled with the mouse.
Foldable
Foldable (also called flexible) keyboards are made of soft plastic or
silicone which can be rolled or folded on itself for travel.
[2] When in use, these keyboards can conform to
uneven surfaces, and are more resistant to liquids than standard keyboards. These can also be connected to portable devices and
smartphones. Some models can be fully immersed in water, making them popular in hospitals and laboratories, as they can be disinfected.
Projection/Laser
Projection keyboards project an image of keys, usually with a laser, onto a flat surface. The device then uses a camera or infrared sensor to "watch" where the user's fingers move, and will count a key as being pressed when it "sees" the user's finger touch the projected image. Projection keyboards can simulate a full size keyboard from a very small projector. Because the "keys' are simply projected images, they cannot be felt when pressed. Users of projected keyboards often experience increased discomfort in their fingertips because of the lack of "give" when typing. A flat, non-reflective surface is also required for the keys to be projected onto. Most projection keyboards are made for use with
PDAs due to their small form factor.
Optical keyboard technology
Also known as photo-optical keyboard, light responsive keyboard, Photo-electric keyboard and optical key actuation detection technology.
An optical keyboard technology utilizes
light emitting devices and
photo sensors to optically detect actuated keys. Most commonly the emitters and sensors are located in the perimeter, mounted on a small
PCB. The
light is directed from side to side of the keyboard interior and it can only be blocked by the actuated keys. Most optical keyboards require at least 2 beams (most commonly vertical beam and horizontal beam) to determine the actuated key. Some optical keyboards use a special key structure that blocks the light in a certain pattern, allowing only one beam per row of keys (most commonly horizontal beam).
http://en.wikipedia.org/wiki/Keyboard_%28computing%29
07-26-10
