Computer keyboard
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 a 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 for environments with space constraints.
Standard arrangements
The most common arrangements in Western countries are based on the
QWERTY layout or closely-related
French AZERTY and
German QWERTZ variants. The layout of the keys in countries with different
alphabets or writing systems, is often similar (e.g. the
Thai keyboard layout).
Most modern computer keyboards are based on standard versions with additional keys not normally found on typewriters, such as
function keys and a
numeric keypad. "Internet keyboards" include extra buttons for user-defined functions such as starting a
web browser or
e-mail client.
Plug types
There are a few different ways of connecting a keyboard which have evolved over the years. These include the standard AT connector commonly found on pre-80486 motherboards, which evolved to the now common
PS/2 and
USB connections. Prior to the iMac line of systems, Apple Computer used ADB, a proprietary system, for its keyboard connector.
Alternatives
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.
|
Microsoft On-Screen Keyboard is software designed for users with limited mobility. |
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 keypresses is generally left to the software. Modern keyboards distinguish each physical key from every other and report all keypresses 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.
Commands
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.
Games
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 keypress 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.
The following briefly describes a "
dome-switch" keyboard (sometimes misleadingly referred to as a
membrane keyboard), the most common type in use today:-
# When a key is pressed, it pushes down on a rubber dome sitting beneath the key. A
conductive contact on the underside of the dome touches (and hence connects) a pair of conductive lines on the circuit below.# This bridges the gap between them and allows current to flow (i.e. the
circuit goes from open to closed), changing the signal strength.# A scanning signal is emitted by the chip along the pairs of lines to all the keys. When the signal in one pair becomes different, the chip generates a "make code" corresponding to the key connected to that pair of lines. # The code generated is sent to the computer either via a keyboard cable (using on-off electrical pulses to represent
bits) or over a
wireless connection.# A chip inside the computer receives the signal bits and decodes them into the appropriate keypress. The computer then decides what to do on the basis of the key pressed (e.g. display a character on the screen, or perform some action).
Other types of keyboard function in a similar manner, the main differences being how the individual key-switches work. For more detail, refer to the "
Keyboard technology" article.
*
Modifier key**
Control key**
Shift key**
Alt key /
Option key (Macintosh)
**
AltGr key**
Command key /
Meta key (MIT computer keyboards)
**
Windows key**
Fn key (Compact keyboards)
*
Dead key**
Compose key*
Lock key**
Scroll lock**
Num lock**
Caps lock*Navigation keys
**
Arrow keys**
Page Scroll (
Page Up /
Page Down)
**
Home key /
End key*
Edit keys**
Return key / Enter key**
Backspace**
Insert key**
Delete key**
Tab*
SysRq /
Print screen*
Break key / Pause key
*
Escape key*
Menu key*
Space bar*
Numpad*
Function key*
Power management keys**Power key
**Sleep key
**Wake key
*
Ergonomics*
Repetitive strain injury* Keyboard styles
**
Alphanumeric keyboard**
Enhanced keyboard***
AT keyboard**
Velotype (chorded keyboard)
**
Virtual keyboard**
Optimus Keyboard**
Das Keyboard (blank keyboard)
**
EZ-Reach (keyboard)*
Keyboard layout**
Dvorak keyboard**
Colemak**
Maltron keyboard*
Keyboard technology**
Membrane keyboard**
Chiclet keyboard**
Buckling spring*
Apple keyboard*
ASCII*
ASDF (sequence of letters)*
British and American keyboards*
Chinese input methods for computers*
Chord keyset*
F-Lock*
GKOS keyboard (chorded keyboard)
*
IBM PC keyboard*
IBM Model M Keyboard*
Microsoft Natural keyboard*
Space-cadet keyboard*
Touch typing*
Typing*
Hunt and peck typing*
Home row*
Key jamming*
Article on Howstuffworks*
Interfacing the AT keyboard *
Keyboard and mouse interfaces pinouts*
Ergonomics research on alternative keyboard designs*
Repair4Keyboard - A survey of do-it-yourself guides about repairing and modding computer keyboards.
