Computer keyboard
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A computer keyboard is a peripheral modeled after the typewriter
keyboard. Keyboards are designed for the input of text and
characters, and also to control the operation of the computer.
Physically, computer keyboards are an arrangement of rectangular or
near-rectangular buttons, or "keys". Keyboards typically have
characters engraved or printed on the keys; in most cases, each
press of a key corresponds to a single written symbol. However, to
produce some symbols requires pressing and holding several keys
simultaneously, or in sequence; other keys do not produce any
symbol, but instead affect the operation of the computer, or the
keyboard itself. See input method editor.
Roughly 50% of all keyboard keys produce letters, numbers or signs
(characters). Other keys can produce actions when pressed, and other
actions are available by simultaneously pressing more than one
action key.
There exist a large number of different arrangements of symbols on
keys. These different keyboard layouts arise because different
people need easy access to different symbols; typically, this is
because they are writing in different languages, but specialized
keyboard layouts for mathematics, accounting, and computer
programming do exist. |
The number of keys on a keyboard generally varies from the standard
101 keys to the 104 windows keyboards all the way up to 130 keys
with many programmable keys. There are also compact variants that
have fewer than 90 keys. They are normally found in laptops or in
desktop computers with space constraints.
The most common arrangements in Western countries are based on the
QWERTY layout (including closely-related variants, such as the
French AZERTY layout). Even in countries where different alphabets
or writing systems are in use, the physical layout of the keys is
often quite similar (e.g. the Thai keyboard layout).
Most modern computer keyboards (including those on the PC and Apple
Mac) are based on these standard versions, but include additional
keys not normally found on typewriters, such as function keys, a
numeric keypad, and so on. In recent years, so-called "Internet
keyboards" have also become popular. These include extra buttons for
specific applications or functions (typically a browser or email
client).
There are a few different ways of connecting a keyboard which have
evolved over the years. These include PS/2 and USB connections.
A standard keyboard is physically quite large, as each key must
remain large enough to be easily pressed by fingers. Other types of
keyboards have been proposed for small portable equipment where a
standard keyboard is too large. One way to reduce the number of keys
is to use chording, i.e. pressing several keys simultaneously. As an
example, the GKOS keyboard has been designed for small wireless
devices. Other two-handed alternatives more akin to a gaming
controller, such as the AlphaGrip, are also used as a way to input
data and text.
In normal usage, the keyboard is used to type text into word
processor, text editor, or any other textbox.
In modern computers the interpretation of key presses is generally
left to the software. Modern keyboards distinguish each physical key
from every other and report all key presses and releases to the
controlling software. This flexibility is not often taken advantage
of and it usually does not matter, for example, whether the left or
right shift key is held down in conjunction with another character.
A keyboard is also used to type commands in a computer. One famous
example on the PC is the Ctrl+Alt+Del combination. With current
versions of Windows, this brings up a menu-window including options
for handling currently-running applications and shutting down the
computer, amongst other things. Under Linux, MS-DOS and some older
versions of Windows, Ctrl+Alt+Del performs either a 'cold' or 'warm'
reboot.
A keyboard is one of the primary methods of control in computer
games. For instance, the arrow keys or a group of letters resembling
the pattern of the arrow keys, like WASD, can be used for movement
of a game character. In many games keys can be configured to the
user's preferences. Alphabet keys are also sometimes used to perform
actions starting with that letter. (e.g. pressing e to eat in
NetHack). Keyboards are less than ideal when many keys are to be
pressed at once, as the limited circuitry means that only a certain
number of keys will register at one time. An obvious example of this
is phantom key blocking. On older keyboards, due to the circuit
design, sometimes pressing three keys simultaneously results in a
4th key press being registered. Modern keyboards prevent this from
happening by blocking the 3rd key in certain key combinations, but
while this prevents phantom input, it also means that when two keys
are depressed simultaneously, many of the other keys on the keyboard
will not respond until one of the two depressed keys is lifted.
Better keyboards are designed so that this happens infrequently in
office programs, but it remains a problem in games even on expensive
keyboards, due to wildly different and/or configurable key/command
layouts in different games. |
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