Wikipedia

Computer keyboard

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A computer keyboard is a peripheral modelled 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.

A 102-key PC US English keyboard layout

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.

Designs

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 specialised keyboard layouts for mathematical, accounting, or computer-programming use do exist.

Standard arrangement

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 the above, 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).

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.

Usage

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. The most famous being Ctrl+Alt+Del on Windows PCs, used for various tasks which are useful should a program freeze. Many other commands for a variety of tasks also exist.

Games

A keyboard is one of the primary controllers in a computer game, and various groups of keys perform game actions. For instance, a group of letters resembling the pattern of the arrow keys, like WASD, is used for movement. Keys can usually be configured to the user's preferences. Alphabet keys are also used to do actions starting with that letter. (e.g. pressing e to eat in game Nethack). Keyboards are less than ideal when many keys are pressed at once, as the limited circuitry means that only a certain number of keys will register at one time. This number depends on where on the keyboard the keys are located.

The number of keys in a keyboard 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.

How it works

The following briefly describes a 'dome switch' keyboard (sometimes misleadingly referred to as a membrane keyboard), the most common type in use today:-

  1. 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.
  2. This bridges the gap between them and allows current to flow (i.e. the switch goes from open to closed), changing the signal strength.
  3. 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.
  4. 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.
  5. 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.

See also

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