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.

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.

Standard Arrangements

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 Arrangements

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. 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.

(Information found on wikipedia. All text is available under the terms of the GNU Free Documentation License - see wikipedia's Copyrights for details).