Input devices allow the user to input data and instructions to the computer. There are a variety of input devices. Direct entry of data generally requires a keyboard. It may also use other devices for direct data entry like a touch sensitive screen, voice recognition system and scanners. The popular input devices are discussed in the following section.
1.      Keyboard:
Keyboard is the most popular input device for direct entry of data and instructions into computer. The standard QWERTY keyboard is used for computer. The enhanced keyboard has 101 keys. In addition to them, the computer keyboard usually has special keys like PageUp, PageDown, PrintScreen etc. The computer keyboard is very much like the electronic typewriter keyboard. But it has additional keys.
Computer keyboard has three types of keys:
 • Alphanumeric keys for typing character and numeric data
• Punctuation keys like comma, period, colon, semicolon, question mark etc.
 • Special keys like function keys, control keys, arrow keys, caps lock etc.
The keyboard is linked to the CPU and it is also linked to the computer screen so that the data entered into the memory can be seen by the user as he types in the data.
2.      Mouse:
A mouse is a small hand-held 'point and click' device that is connected to the CPU through a cable. Douglas Engelbart invented mouse in 1963at Stanford Research Institute. Xerox Corporation's Palo Alto Research Center enhanced its capabilities by adding analogue to digital conversion. In the early 1970's. With the adoption of Graphical User Interface technology, mouse became an essential input device for computer later in the 1980's.
There are three types of mouse:
i: mechanical
ii :optomechanical
The mechanical mouse has a trackball at its bottom. It can be rolled across a flat and smooth surface to control the position of the cursor on the screen. By pointing and clicking on icons and menu options displayed on the screen, it is easy for the user to control the computer with a mouse. Mechanical sensors within the mouse detect the direction the ball is rolling and move the screen pointer accordingly.
The optomechanical mouse is more or less the same as the mechanical mouse, but it uses optical sensors to detect motion of the ball.
Optical mouse uses a laser to detect the mouse movement. The mouse requires to be moved along a special mat with a grid so that the optical mechanism has a frame of reference. It has no mechanical moving parts. It responds more quickly and precisely than mechanical or optomechanical mouse. Optical mouse is more expensive than the other two.
3.     Light Pen
Light pen consists of a stylus connected by a cable to the computer terminal. When the stylus is brought into contact with the screen, a dot appears there on the screen. By moving the stylus on the screen, lines and curves can be drawn on the screen that can be stored and used as input.
4.      Trackball
Trackball was originally built into the keyboard. Running a hand over the trackball made the cursor on the screen to move. The cursor is used to make selection from a menu displayed on the computer screen.
5.      Joystick
 Joystick is a small vertical stick attached to a trackball for easier mechanical movements. It is used mainly in game programs.
6.     Scanners
Scanners are direct-entry input devices. As the data entry is automatic, the scanners ensure more accurate data entry. These scanners include optical scanners and magnetic ink character readers. The optical scanners use light for sensing input and they include OCR, OMR and Barcode reader.
7.  Optical Mark Reader
 Optical mark reader (OMR) reads the presence or absence of a mark on a paper optically. Light is directed on to the paper and the reflected light is analysed for the detection of a mark. If a mark is there on the surface of the paper, that area sends back lesser light are to the OMR. It is used to read multiple choice answers in a test and the data are transferred to a computer for processing.
  8.  Optical Character Reader
 Optical character reader (OCR) detects shape, and can identify characters. It can examine each character as if it were made up of a collection of minute spots. Once the whole character has been scanned, the pattern detected is matched against a set of patterns stored in the computer. The pattern that matches or nearly matches is taken to be the character read. Patterns that cannot be identified are rejected. It is used in mail sorting and credit card billing.
9. Barcode Reader
 Barcode is a set of small bars of varying thickness and spacing printed on the packages of products, on the back cover pages of books, tags etc. The barcode reader uses an optical scanner to read product code and converts it into electrical pulses. The device is connected to a computer and the information read is passed to the computer in digital form for automatic bill generation and updating of files. Thus, it is a direct data entry device and there is no need for an operator to key in sales transaction data.
10. Magnetic Ink Character Recognition
Magnetic Ink Character Recognition (MICR) uses highly stylised character shapes printed in a special ink containing particles that can be magneti~ed. This ink induces a current in a reading circuit, which is proportional to the area of ink being scanned. The patterns of the varying currents can be compared with and selected as bit patterns of the selected number e.g., the number on a cheque). The MICR reader can only identify characters. Banking industry uses this device for sorting of cheques. The MICR codes read from the cheques are transmitted to an online computer for sorting and processing automatically.
11. Tag Reader
 Retail clothing units use a tag reader system. Clothes have price tags with data coded on card tags. The tag reader decodes it and passes the data into the computer connected to it for billing and file updating. Point of Sale Terminal (POS Terminal) The POS terminal consists of a numeric keypad and a few control or function keys. The operator at the point of sale enters the product code and quantity purchased by a customer. The terminal generates bill and, if connected to a computer, the system updates the related files automatically.
12.  Voice Recognition Systems
 A special microphone is used to capture voice .input. It converts the voice into electrical pulses and then into digital signals for onward transmission to a computer for processing. A voice recognition system is provided with digital patterns of a limited vocabulary of words and phrases. The system operating in a training mode learns to recognise voice patterns by comparing the spoken input with the stored digital patterns. After identifying the input, the voice system generates' appropriate code for the machine to accept input and operate. Voice recognition systems are very useful in offices for word processing. A manager can directly dictate letters and r.otes to a word processor through a speech recognition system. Similarly, the system can accept oral commands and execute them. These systems are yet to become popular.
13.  Graphic Tablet
 This is a flat surface input device, which is attached to the computer like a mouse. Its surface is pressure sensitive. A special pen is used against the surface of the tablet and the cursor moves in response to the movements of the pen on the tablet. This input device is particularly useful for graphic artists.
14.  Digital Cameras
Digital cameras are used to capture images and they can record the images on reusable floppy disks. Images are used with a digitiser for input to the computer. Once the image input is stored in computer, the image can be used in any application.
15. Vision Systems
A computer can be equipped with sensors to 'see' objects around. Robots with vision systems are used in industrial engineering. They are used in complex operations like assembling components requiring great precision.