Computer keyboard
In computing, a
keyboard is a typewriter-style device, which uses an arrangement of buttons or
keys, to act as mechanical levers or electronic switches. Following the decline
of punch cards and paper tape, interaction via tele printer-style keyboards became
the main input device for computers.
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
execute computer commands.
Despite the
development of alternative input devices, such as the mouse, touch screen, pen
devices, character recognition and voice recognition, the keyboard remains the
most commonly used device for direct (human) input of alphanumeric data into
computers.
In normal usage,
the keyboard is used as a text entry interface to type text and numbers into a
word processor, text editor or other programs. In a modern computer, the
interpretation of key presses is generally left to the software. A computer
keyboard distinguishes each physical key from every other and reports all key
presses 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. A command-line interface is a type of user interface operated entirely
through a keyboard, or another device doing the job of one.
History
While typewriters are the definitive ancestor of all
key-based text entry devices, the computer keyboard as a device for
electromechanical data entry and communication derives largely from the utility
of two devices: tele printers (or teletypes) and keypunches. It was through
such devices that modern computer keyboards inherited their layouts.
As early as the 1870s, teleprinter-like devices were used to
simultaneously type and transmit stock market text data from the keyboard
across telegraph lines tostock ticker machines to be immediately copied and
displayed onto ticker tape. The teleprinter, in its more contemporary form, was
developed from 1907 to 1910 by American mechanical engineer Charles Krum and
his son Howard, with early contributions by electrical engineer Frank Pearne.
Earlier models were developed separately by individuals such as Royal Earl
House and Frederick G. Creed.
Earlier, Herman Hollerith developed the first keypunch
devices, which soon evolved to include keys for text and number entry akin to
normal typewriters by the 1930s.
The keyboard on the
teleprinter played a strong role in point-to-point and point-to-multipoint
communication for most of the 20th century, while the keyboard on the keypunch
device played a strong role in data entry and storage for just as long. The
development of the earliest computers incorporated electric typewriter
keyboards: the development of the ENIAC computer incorporated a keypunch device
as both the input and paper-based output device, while the BINAC computer also
made use of an electromechanically controlled typewriter for both data entry
onto magnetic tape (instead of paper) and data output.
From the 1940s until the late 1960s, typewriters were the
main means of data entry and output for computing, becoming integrated into
what were known ascomputer terminals. Because of the limitations of terminals
based upon printed text in comparison to the growth in data storage, processing
and transmission, a general move toward video-based computer terminals was
affected by the 1970s, starting with the Data point 3300 in 1967.
The keyboard remained the primary, most integrated computer
peripheral well into the era of personal computing until the introduction of
the mouse as a consumer device in 1984. By this time, text-only user interfaces
with sparse graphics gave way to comparatively graphics-rich icons on screen.
However, keyboards remain central to human-computer interaction to the present,
even as mobile personal computing devices such as smart phones and tablets
adapt the keyboard as an optional virtual, touch screen-based means of data
entry.
Keyboard
types
One factor
determining the size of a keyboard is the presence of duplicate keys, such as a
separate numeric keyboard, for convenience.
Further the
keyboard size depends on the extent to which a system is used where a single
action is produced by a combination of subsequent or simultaneous keystrokes
(with modifier keys, see below), or multiple pressing of a single key. A
keyboard with few keys is called a keypad. See also text entry interface.
Another factor
determining the size of a keyboard is the size and spacing of the keys.
Reduction is limited by the practical consideration that the keys must be large
enough to be easily pressed by fingers. Alternatively a tool is used for
pressing small keys.
Standard
Standard alphanumeric keyboards have keys that are on
three-quarter inch centers (0.750 inches, 19.05 mm)[citation needed], 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, such as the command or Windows keys.
Laptop-size
Keyboards on laptops and notebook computers usually have a
shorter travel distance for the keystroke, shorter over travel distance, 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. The switch mechanism for a laptop keyboard is more likely
to be a scissor switch than a rubber dome; this is opposite the trend for
full-size keyboards.
Handheld
Handheld ergonomic keyboards are designed to be held like a
game controller, and can be used as such, instead of laid out flat on top of a
table surface. Typically handheld keyboards hold all the alphanumeric keys and
symbols that a standard keyboard would have, yet only be accessed by pressing
two sets of keys at once; one acting as a function key similar to a 'Shift' key
that would allow for capital letters on a standard keyboard.[1] Handheld
keyboards allow the user the ability to move around a room or to lean back on a
chair while also being able to type in front or away from the computer.[2] Some
variations of handheld ergonomic keyboards also include a trackball mouse that
allow mouse movement and typing included in one handheld device.
Thumb-sized
Smaller external
keyboards have been introduced for devices without a built-in keyboard, such as
PDAs, and smart phones. Small keyboards are also useful where there is a
limited workspace.
A chorded keyboard
allows users to press 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 Alpha Grip, are also
used to input data and text.
A thumb keyboard
(thumb board) 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, numbers,
Arrow keys, Navigation keys, Num Lock and Enter key.
Non-standard layout and
special-use types
While other keyboards generally associate one action with
each key, chorded keyboards associate actions with combinations of key presses.
Since there are many combinations available, chorded keyboards can effectively
produce more actions on a board with fewer keys. Court reporters' stenotype
machines use chorded keyboards to enable them to enter text much faster by
typing a syllable with each stroke instead of one letter at a time. The fastest
typists (as of 2007) use a stenograph, a kind of chorded keyboard used by most
court reporters and closed-caption reporters. Some chorded keyboards are also
made for use in situations where fewer keys are preferable, such as on devices
that can be used with only one hand, and on small mobile devices that don't
have room for larger keyboards. Chorded keyboards are less desirable in many
cases because it usually takes practice and memorization of the combinations to
become proficient.
Software
Software keyboards
or on-screen keyboards often take the form of computer programs that display an
image of a keyboard on the screen. Another input device such as a mouse or a
touchscreen can be used to operate each virtual key to enter text. Software
keyboards have become very popular in touchscreen enabled cell phones, due to
the additional cost and space requirements of other types of hardware
keyboards. Microsoft Windows, Mac OS X, and some varieties of Linux include
on-screen keyboards that can be controlled with the mouse. In software keyboards,
the mouse has to be maneuvered onto the on-screen letters given by the
software. On the click of a letter, the software writes the respective letter
on the respective spot.
Projection
(as by laser)
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, and will count a key as
being pressed when it "sees" the user's finger touch the projected
image. Projection keyboards can simulate a full size keyboard from a very small
projector. Because the "keys" are simply projected images, they
cannot be felt when pressed. Users of projected keyboards often experience
increased discomfort in their fingertips because of the lack of "give"
when typing. A flat, non-reflective surface is also required for the keys to be
projected. Most projection keyboards are made for use with PDAs and smartphones
due to their small form factor.
Optical
keyboard technology
Also 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. Most
optical keyboards require at least 2 beams (most commonly vertical beam and
horizontal beam) to determine the actuated key. Some optical keyboards use a
special key structure that blocks the light in a certain pattern, allowing only
one beam per row of keys (most commonly horizontal beam).
Further information: Keyboard technology
Layout
Alphabetic
There are a number
of different arrangements of alphabetic, numeric, and punctuation symbols on
keys. These differentkeyboard 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,[3] Mac OS X[4] and Linux.[5][6] The common
QWERTY-based layout was designed early in the era of mechanical typewriters, so
its ergonomics were compromised to allow for 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 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 Portuguese, 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. Japanese layout keyboards can be switched between various Japanese
input methods and the Latin alphabet by signaling the operating system's input
interpreter of the change, and some operating systems (namely the Windows
family) interpret the character "\" as "¥" for display
purposes without changing the bytecode which has led some keyboard makers to
mark "\" as "¥" or both. 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; 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
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.
Modifier
keys
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 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). 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.
Cursor keys
Navigation keys or cursor 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. TheInsert 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. TheBackspace 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 numeric
pad. The lock keys includeScroll lock, Num lock (which allows the use of the
numeric keypad), and Caps lock.
System commands
The SysRq and Print screen commands often share the same
key. SysRq was used in earlier computers as a "panic" button to
recover from crashes (and it is still used in this sense to some extent by the
Linux kernel; see Magic SysRq key). 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 teleprinter 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 "escape"
or back out of a mistaken command. 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, Vista, 7,
and 8. The Enter key is located: One in the alphanumeric keys and the other one
is in the numeric keys. When one worked something on their computer and wanted
to do something with their work, pressing the enter key would do the command
they ordered. Another function is to create a space for next paragraph. When
one typed and finished typing a paragraph and they wanted to have a second
paragraph, they could press enter and it would do spacing. Shift key: when one
presses shift and a letter, it will capitalize the letter pressed with the
shift key. Another use is to type more symbols than appear to be available, for
instance the apostrophe key is accompanied with a quotation mark on the top. If
one wants to type the quotation mark but pressed that key alone, the symbol
that would appear would be the apostrophe. The quotation mark will only appear
if both the required key and the Shift key are pressed. 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 usually a small icon depicting a cursor
hovering above a menu. On some Samsung keyboards the cursor in the icon is not
present, showing the menu only. 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
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 for
changing the language to use. 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 or keys that can be
programmed by the user to launch a specified software or command like launching
a game or minimize all windows.
Numeric keys
When we calculate, we use these numeric keys to type
numbers. Symbols concerned with calculations such as addition, subtraction,
multiplication and division symbols are located in this group of keys. The
enter key in this keys indicate the equal sign.
Multiple layouts
It is possible to install multiple keyboard layouts within
an operating system and switch between them, either through features
implemented within the OS, or through an external application. Microsoft
Windows,[7] Linux,[8] and Mac[9] provide support to add keyboard layouts and
choose from them.
Layout
changing software
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. Many programs are available, some of which
are language specific.
The arrangement of symbols of specific language can be
customized. An existing keyboard layout can be edited, and a new layout can be
created using this type of software.
For example, Ukelele for Mac,[10] The Microsoft Keyboard
Layout Creator[11] and open-source Avro Keyboard for Windows provide the
ability to customize the keyboard layout as desired.
Illumination
Keyboards and keypads may be illuminated from inside,
especially on equipment for mobile use. Illumination facilitates the use of the
keyboard or keypad in dark environments. Some gaming keyboards have lighted
keys, to make it easier for gamers to find command keys while playing in a dark
room. Some computers may have small LED lights in a few important function
keys, to remind users that the function is activated (see photo).
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