Keyboard

Keyboard

Keyboard is an input device, partially modeled after the typewriter 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 keypresses is generally left to the software. A computer keyboard distinguishes each physical key from every other and reports all keypresses to the controlling software. Keyboards are also used for computer gaming, either with regular keyboards or by using keyboards with special gaming features, which can expedite frequently used keystroke combinations. A keyboard is also used to give commands to the operating system of a computer, such as Windows' Control-Alt-Delete combination, which brings up a task window or shuts down the machine.

Types Of Keyboard

Standard
Standard keyboards for desktop computers, 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).Computer keyboards are similar to electric-typewriter keyboards but contain additional keys.
Laptop-size
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.
Multimedia
Keyboards with extra keys, such as multimedia keyboards, have special keys for accessing music, web and other frequently used programs. For example, 'ctrl+marked on color-coded keys are used for some software applications and for specialized uses such as video editing.
Thumb-sized
Smaller keyboards have been introduced for laptops, PDAs, cellphones or users who have a limited workspace. The size of a standard keyboard is dictated by the practical consideration that the keys must be large enough to be easily pressed by fingers. To reduce the size of the keyboard, the numeric keyboard to the right of the alphabetic keyboard can be removed, or the size of the keys can be reduced, which makes it harder to enter text.
Another way to reduce the size of the keyboard is to reduce the number of keys and use chording keyer, i.e. pressing several keys simultaneously. For example, the GKOS keyboard has been designed for small wireless devices. Other two-handed alternatives more akin to a game controller, such as the AlphaGrip, are also used as a way to input data and text. Another way to reduce the size of a keyboard is to use smaller buttons and pack them closer together. Such keyboards, often called a "thumbboard" (thumbing) are used in some personal digital assistants such as the Palm Treo and BlackBerry and some Ultra-Mobile PCs such as the OQO.
Numeric
Numeric keyboards contain only numbers, mathematical symbols for addition, subtraction, multiplication, and division, a decimal point, and several function keys (e.g. End, Delete, etc.). They are often used to facilitate data entry with smaller keyboard-equipped laptops or with smaller keyboards that do not have a numeric keypad. A laptop does sometimes have a numeric pad, but not all the time. These keys are also known as, collectively, 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

Layout Of Keyboard

Alphabetic

The 104-key PC US English QWERTY keyboard layout evolved from the standard typewriter keyboard, with extra keys for computing.
The Dvorak Simplified Keyboard layout arranges keys so that frequently used keys are easiest to press, which reduces muscle fatigue when typing common English.
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. Most of the more common keyboard layouts (QWERTY-based and similar) were designed in the era of the mechanical typewriters, so their ergonomics had to be slightly compromised in order to tackle some of the mechanical limitations of the typewriter.
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. With the advent of computers, lever jams are no longer an issue, but nevertheless, QWERTY layouts were adopted for electronic keyboards because they were widely used. Alternative layouts such as the Dvorak Simplified Keyboard are not in widespread use.
The QWERTZ layout is fairly 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.
Another situation takes place with “national” layouts. Keyboards designed for typing in Spanish have some characters shifted, to release the space for Ñ ñ; similarly, those for French and other European languages may have a special key for the character Ç ç . The AZERTY layout is used in France, Belgium and some neighbouring countries. It differs from the QWERTY layout in that the A and Q are swapped, the Z and W are swapped, and the M is moved from the right of N to the right of L (where colon/semicolon is on a US keyboard). The digits 0 to 9 are on the same keys, but to be typed the shift key must be pressed. The unshifted positions are used for accented characters.
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, and the character ¥ (the Yen currency) is used instead of "\". In the Arab world, keyboards can often be switched between Arabic and English.
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; while both keyboards share the same QWERTY alphabetic layout, the French-language keyboard enables the user to type accented vowels such as "é" or "à" with a single keystroke. Using keyboards for other languages leads to a conflict: the image on the key does not correspond to the character. In such cases, each new language may require an additional label on the keys, because the standard keyboard layouts do not share even similar characters of different languages (see the example in the figure above).
Key Types
Alphanumeric
A Hebrew keyboard lets the user type in both Hebrew and the Latin alphabet.
A Greek keyboard lets the user type in both Greek and the Latin alphabet(Macbook Pro).
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. Many of these keys will produce different symbols when modifier keys or shift keys are pressed. The alphabetic characters become uppercase when the shift key or Caps Lock key is depressed. The numeric characters become symbols or punctuation marks when the shift key is depressed. The alphabetical, numeric, and punctuation keys can also have other functions when they are pressed at the same time as some modifier keys.
The Space bar is a horizontal bar in the lowermost row, which is significantly wider than other keys. Like the alphanumeric characters, it is also descended from the mechanical typewriter. Its main purpose is to enter the space between words during typing. It is large enough so that a thumb from either hand can use it easily. Depending on the operating system, when the space bar is used with a modifier key such as the control key, it may have functions such as resizing or closing the current window, half-spacing, or backspacing. In computer games and other applications the key has myriad uses in addition to its normal purpose in typing, such as jumping and adding marks to check boxes. In certain programs for playback of digital video, the space bar is used for pausing and resuming the playback.
Modifiers
Modifier keys are special keys that modify the normal action of another key, when the two are pressed in combination. For example, <Alt> + <F4> in Microsoft Windows will close the program in an active window. In contrast, pressing just <F4> will probably do nothing, unless assigned a specific function in a particular program. By themselves, modifier keys usually do nothing.
The Ctrl and Alt keys are important modifier keys.
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. On MIT computer keyboards, the Meta key is used as a modifier and 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).
A Space-cadet keyboard has many modifier keys.
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 and typing mode
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. The 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.
System commands
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/Pause key no longer has a well-defined purpose. Its origins go back to teletype users, who wanted a key that would temporarily interrupt the communications line. 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. As most computer users no longer are concerned with the details of controlling their computer's peripherals, the task for which the escape sequences were originally designed, the escape key was appropriated by application programmers, most often to mean Stop. This use continues today in Microsoft Windows's use of escape as a shortcut in dialog boxes for No, Quit, Exit, Cancel, or Abort.
A common application today of the Esc key is as a shortcut key for the Stop button in many web browsers. On machines running Microsoft Windows, prior to the implementation of the Windows key on keyboards, the typical practice for invoking the "start" button was to hold down the control key and press escape. This process still works in Windows 2000, XP, Windows Vista and Windows 7.
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 key's symbol is a small icon depicting a cursor hovering above a menu. This key was created at the same time as the Windows key. This key is normally used when the right mouse button is not present on the mouse. Some Windows public terminals do not have a Menu key on their keyboard to prevent users from right-clicking (however, in many windows applications, a similar functionality can be invoked with the Shift+F10 keyboard shortcut).
Miscellaneous
Multimedia buttons on some keyboards give quick access to the Internet or control the volume of the speakers.
Many, but not all, computer keyboards have a numeric keypad to the right of the alphabetic keyboard which contains numbers, basic mathematical symbols (e.g., addition, subtraction, etc), and a few function keys. On Japanese/Korean keyboards, there may be Language input keys. Some keyboards have power management keys (e.g., Power key, Sleep key and Wake key); Internet keys to access a web browser or E-mail; and/or multimedia keys, such as volume controls.

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