KEYBOARD




In computing, a keyboard is a typewriter-style keyboard, which uses an arrangement of buttons or keys, to act as mechanical levers or electronic switches.

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 keyboard is also used to give commands to the operating system of a computer, such as Windows’ Control-Alt-Delete combination

Keyboards are the only way to enter commands on a command-line interface.

A keyboard with few keys is called a keypad.

Standard “full-travel” alphanumeric keyboards have keys that are on three-quarter inch centers (0.750 inches, 19.05 mm), and have a key travel of at least 0.150 inches (3.81 mm). Desktop computer keyboards, such as the 101-key US traditional keyboards or the 104-key Windows keyboards, include alphabetic characters, punctuation symbols, numbers and a variety of function keys. The internationally common 102/105 key keyboards have a smaller ‘left shift’ key and an additional key with some more symbols between that and the letter to its right (usually Z or Y). Also the ‘enter’ key is usually shaped differently. Computer keyboards are similar to electric-typewriter keyboards but contain additional keys. Standard USB keyboards can also be connected to some non-desktop devices

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.

A chorded keyboard allows pressing several keys simultaneously. For example, the GKOS keyboard has been designed for small wireless devices.

A thumb keyboard (thumbboard) is used in some personal digital assistants such as the Palm Treo and BlackBerry and some Ultra-Mobile PCs such as the OQO.

Numeric keyboards contain only numbers, mathematical symbols for addition, subtraction, multiplication, and division, a decimal point, and several function keys. They are often used to facilitate data entry with smaller keyboards that do not have a numeric keypad, commonly those of laptop computers. These keys are collectively known as 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.

Software keyboards or on-screen keyboards often take the form of computer programs that display an image of a keyboard on the screen.

Foldable (also called flexible) keyboards are made of soft plastic or silicone which can be rolled or folded on itself for travel

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

An optical keyboard 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.

There are a number of different arrangements of alphabetic, numeric, and punctuation symbols on keys. These different keyboard layouts arise mainly because different people need easy access to different symbols, either because they are inputting text in different languages, or because they need a specialized layout for mathematics, accounting, computer programming, or other purposes.

The United States keyboard layout is used as default in the currently most popular operating systems: Windows,[4] Mac OS X and Linux.

As the letter-keys were attached to levers that needed to move freely, inventor Christopher Sholes developed the QWERTY layout to reduce the likelihood of jamming.

The QWERTZ layout is widely used in Germany and much of Central Europe. The main difference between it and QWERTY is that Y and Z are swapped, and most special characters such as brackets are replaced by diacritical characters.

The AZERTY layout is used in France, Belgium and some neighbouring countries.

Keyboards in many parts of Asia may have special keys to switch between the Latin character set and a completely different typing system. In Japan, keyboards often can be switched between Japanese and the Latin alphabet. In the Arab world, keyboards can often be switched between Arabic and Latin characters.

In bilingual regions of Canada and in the French-speaking province of Québec, keyboards can often be switched between an English and a French-language keyboard

KEY TYPES
Alphabetical, numeric, and punctuation keys are used in the same fashion as a typewriter keyboard to enter their respective symbol into a word processing program, text editor, data spreadsheet, or other program.

The Space bar is a horizontal bar in the lowermost row, which is significantly wider than other keys.

Modifier keys are special keys that modify the normal action of another key. By themselves, modifier keys usually do nothing.

The most widely used modifier keys include the Control key, Shift key and the Alt key. The AltGr key is used to access additional symbols for keys that have three symbols printed on them.

On the Macintosh and Apple keyboards, the modifier keys are the Option key and Command key, respectively.

For Windows keyboards, there is a Windows key. Compact keyboard layouts often use a Fn key.

“Dead keys” allow placement of a diacritic mark, such as an accent, on the following letter (e.g., the Compose key).

The Enter/Return key typically causes a command line, window form or dialog box to operate its default function, which is typically to finish an “entry” and begin the desired process. In word processing applications, pressing the enter key ends a paragraph and starts a new one.

Navigation keys include a variety of keys which move the cursor to different positions on the screen. Arrow keys are programmed to move the cursor in a specified direction; page scroll keys, such as the ‘Page Up and Page Down keys’, scroll the page up and down. The Home key is used to return the cursor to the beginning of the line where the cursor is located; the End key puts the cursor at the end of the line. The Tab key advances the cursor to the next tab stop.

The Insert key is mainly used to switch between overtype mode, in which the cursor overwrites any text that is present on and after its current location, and insert mode, where the cursor inserts a character at its current position, forcing all characters past it one position further.

Delete key discards the character ahead of the cursor’s position, moving all following characters one position “back” towards the freed place.

On many notebook computer keyboards the key labeled Delete (sometimes Delete and Backspace are printed on the same key) serves the same purpose as a Backspace key. The Backspace key deletes the preceding character.

Lock keys lock part of a keyboard, depending on the settings selected. The lock keys are scattered around the keyboard. Most styles of keyboards have three LEDs indicating which locks are enabled, in the upper right corner above the numpad. The lock keys include Scroll lock, Num lock (which allows the use of the numeric keypad), and Caps lock.

The SysRq / Print screen commands often share the same key. SysRq was used in earlier computers as a “panic” button to recover from crashes. The Print screen command used to capture the entire screen and send it to the printer, but in the present it usually puts a screenshot in the clipboard.

The Break key can be used by software in several different ways, such as to switch between multiple login sessions, to terminate a program, or to interrupt a modem connection.

In programming, especially old DOS-style BASIC, Pascal and C, Break is used (in conjunction with Ctrl) to stop program execution. In addition to this, Linux and variants, as well as many DOS programs, treat this combination the same as Ctrl+C. On modern keyboards, the break key is usually labeled Pause/Break. In most Windows environments, the key combination Windows key+Pause brings up the system properties.

The Escape key (often abbreviated Esc) is used to initiate an escape sequence.

The Menu key or Application key is a key found on Windows-oriented computer keyboards. It is used to launch a context menu with the keyboard rather than with the usual right mouse button.

The character code produced by any key press is determined by the keyboard driver software. A key press generates a scancode which is interpreted as an alphanumeric character or control function. Depending on operating systems, various application programs are available to create, add and switch among keyboard layouts.

Keystroke logging (often called keylogging) is a method of capturing and recording user keystrokes. While it is used legally to measure employee productivity on certain clerical tasks, or by law enforcement agencies to find out about illegal activities, it is also used by hackers for various illegal or malicious acts. Hackers use keyloggers as a means to obtain passwords or encryption keys and thus bypass other security measures.

Related External Links

This entry was posted in Notes and tagged , , , , , , . Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *

*

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>