Input is data put into a computer for processing. Input devices are broken down into 3 categories: keyboards, pointing devices, and Data-Entry devices.
The keyboard is the most popular input device for a computer. It translates numbers, letters, symbols and control keys into signals that can be interpreted by the PC. Most English keyboards today are based on the qwerty design. Some specialist keyboards have extra function keys that perform special actions when pressed. An example is a gaming keyboard seen on the right.
QWERTY is the most common modern-day keyboard layout on English-language computer and typewriter keyboards. It takes its name from the first six letters seen in the keyboard's top first row of letters. The QWERTY design was patented by Christopher Sholes in 1867 and sold to Remington in 1873, when it first appeared in typewriters". "According to popular myth, Sholes arranged the keys in their odd fashion to prevent jamming on mechanical typewriters by separating commonly used letter combinations". 
An alternative to the QWERTY keyboard is the Dvorak keyboard, invented to achieve a more efficient method of typing, since the vowels were kept together. Sadly the Dvorak keyboard never received widespread use because QWERTY had become the de facto standard.
Keyboards may come in wireless, foldable or virtual varieties, as shown on the right
Mouse/Pointing Device 
Another type of input device that uses a pointing, or insertion device instead of characters from a keyboard. With the rise in graphical user interfaces, mice became the most commonly used method in controlling a computer. A mouse is used to manipulate objects and text etc. on the computer screen. This device can be plugged into the back of a computer, the back of a keyboard, or can even be cordless! The mouse was invented by Doug Englebart.
The ball mouse utilizes a small rubber ball inside to transmit a spatial relationship between objects on the screen. The mechanical movement is done by 2 scroll bars that detects X and Y axis movement of the ball to allow it to glide on the desktop plane. The ball mouse was invented by Bill English in 1972.
Since it contained moving parts, the ball mouse was prone to dirt build up inside. Hairs would often get caught and rolled into the ball mechanism, causing the mouse to function erratically. With the falling cost of technology, ball mice have now been mostly replaced with lighter optical mice.
The optical mouse uses a light-emitting diode and photodiodes to detect movement relative to the underlying surface, rather than moving some of its parts like the traditional track ball that detects movement of X and Y axis mechanical movement of the roller stick. In order to increase the precision of the mouse, multiple infrared lasers with increasing resolution are used.
Early optical mice came in two kinds. Type 1) Used an infrared LED and a four-quadrant infrared sensor to detect grid lines printed with infrared absorbing ink on a special metallic surface. Type 2) Used a 16-pixel visible-light image sensor with integrated motion detection on the same chip and tracked the motion of light dots in a dark field of a printed paper or similar mouse pad. w:Optical_mouse#Optical_mice
This mouse actually takes 1,500 camera like images per second and the images are sent to a processor to determine changes in the patterns to allow the computer to notice how the position of the mouse has changed and therefore the cursor on the computer screen reacts accordingly. 
Another form of Mouse is a Track Ball, It is somewhat in reverse of a standard mouse. The Track Ball has a platform that is stable and does not move. The ball is on the top side, the user moves the ball with their fingers or thumb. In many ways this can be much more accurate then a standard mouse and requires less space then a mobile mouse as it does not require extra room for movement. The trackball uses numerous optical sensors to track movement often using specially coated ball to help in accuracy.
Touchpad/Pointing Stick 
Touch pads are most commonly built into a laptop computer. A touch pad is a rectangular plastic piece which can control the pointer on a computer simply by dragging your finger across its surface. A pointing stick resembles an pencil eraser and is commonly located in between keys on a laptop key board. To control the pointer on the computer with a pointing stick you use your finger to bend the stick in the direction you would like the pointer to move.
Touchpads were originally known as trackpads. Some touchpads can have multiple mouse buttons by either tapping in a special corner of the pad, or by tapping with two or more fingers. Scrolling is implemented in touchpads along the sides, although this can be configured in touchpad settings. Some touchpads respond to multitouch, like the touchpads found on MacBooks.
A touchpad differs from a point stick in that it allows one to move the cursor about without having to adjust the position of your hand. Some find this more convenient because pressure is not needed to move the sensor. Touchpads are also more accurate, albeit, expensive compared to pointing sticks. Once again due to the virtues of cheaper technology, a touchpad is considered standard on a laptop.
Touch Screen 
By using the touch of a finger on a computer screen, the computer is able to receive input from the movement of your finger to control operations of the computer. The finger transfers electrical currents to the computer. Touch screens are commonly used on ATM machines, bridal directories, and these days at self-checkout stations in places like Wal-Mart.
There are 2 common types of touch screen, resistive screens and capacitive screens. Resistive screen operate by using 2 thin layers. When one layer comes into contact with another (from someone pressing the screen), they form a connection which can be translated into a pair of coordinates a computer uses.
The second technology utilises the concept that the human body is a conductor, and when someone taps on a resisting material (such as a glass panel), a change in capacitance is observed, and the computer can determine where the user made a selection. This type of technology is known as Capacitive sensing. A popular use of capacitative sensing is the touch screens in popular smartphones such as the Iphone.
A Stylus (which is Latin for stake or pointed object) is a small pen-like device used to enter data by reacting to a touch-sensitive screen or film. Styli allow a user to input handwriting specific pieces of information like signatures. Many artists also utilize styli with the use of a tablet.
One important feature of a stylus is its tip which ideally is made of a firm but non-scratching form of plastic. The body of a stylus can be made from anything ranging from synthetic plastic to bronze or chrome in some situations.
Styli are used with many popular devices like Palm Pilots and Trios, Blackberries and Nintendo DSs. Their popularity has reached a point where some company's offer conversion kits to change high-end or ergonomic writing pens into a stylus.
Light Pen 
Light pen is a device which looks like a pen connected to the computer the user can bring the pen to which ever they want to locate.
A computer input device, with a light sensitive wand works with CRT monitors. Used like/for a touch screen with higher They were used in engineering, graphic design and illustrating but light pens have been replaced by other technologies.
A digitizer is a "pointing" technology implemented on computer tablets. It consists of the "tablet", an electronically integrated surface representative (to the computer) of an XY-axis grid. Using the electronic stylus (pen), the tablet will detect the stylus' movements and convert it into digital signals for the computer to use. A digitizing tablet is commonly used in the engineering and architectural industries as well as for fine and commercial art.
A scanner is a device that uses light to read an image or text and turn it into a digital message. This media can then be used to store, change and send the image or text. There are various types of scanners. The three most common are Drum, flatbed and hand. Drum scanners use photomultiplier tubes (PMT). Flatbed scanners use a glass pane and a bright light. Hand scanners are dragged across the
A bar code is a series of stripes that vary in thickness. These stripes represent numbers, which a computer reads as data. Bar codes are printed on products that are sold in retail, as well as postal service packages, rental videos etc. Bar Codes are still in common use today. With the introduction of Wifi enabled smartphones with cameras, barcodes can be scanned on products and matched to an online database which allows someone to compare prices between various retail stores without having to visit each one. Another use of this combination is finding the nutritional content of a consumable product by scanning its barcode.
The first bar code was on a package of Wrigley's Gum in 1974.
Fax which is short for facsimile, is a telecommunications technology used to transfer copies of documents, and was first used through telephone network. Fax is also known as a telecopier in certain industries. A fax machine consists of a scanner, a modem, a printer, and a phone.
Flat Bed 
A flatbed scanner works in a similar fashion to a photocopier. The scanned image is stationary, usually sitting on a piece of glass. The scanning beam then moves across the image to copy the data. The flatbed scanner is also known as a desktop scanner. It can be found combined with printers, due to their low cost.
Speech Recognition 
Input to a computer can take the form of speech. While technology for this is not widespread, speech input is constantly improving, and may find use in everyday life in the near future.
Phonetic models 
Sounds (phonemes) are the basis of words. The computer can identify the sounds and match them with potential words. Word with the same phonemes (their and there) can be selected by the words around them using grammar.
A speech recognition dictionary creation device can create a speech recognition dictionary capable of recognizing even an abbreviated expression of a word with a high recognition ratio. The device consist of: a word separation section for dividing a recognition object speech consisting of one or more words into constituting words, a string acquisition section for creating a string for each of the constituting words according to the reading of the constituting words separated, an abbreviated word creation rule storage section for storing an abbreviated word creation rule using; an abbreviated word creation section for taking a out of a string of each constituting word, joining them so as to create a candidate of an abbreviated word containing one or more and applying the abbreviated word creation rule to the candidates so as to create an abbreviated word; and vocabulary section for storing the created abbreviated word together with the recognition object word as a speech recognition dictionary.
Matching phonemes with words requires the use of grammar. ("their" house, or over "there")