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  • A user interacts with the computer via Input-Output (I/O) devices. The peripheral devices are attached externally to the computer machine.

  • Input unit accepts input data from the user via input device, transforms the input data in computer acceptable form and provides the transformed input data for processing.

  • Output unit accepts output data from computer via output device, transforms the output information to human readable form and provides the transformed output to user.

  • Some devices are both input and output devices. Hard disk drive, floppy disk drive, optical disk drives are examples of input-output devices.

  • Keyboard is used to enter text data. Standard keyboard contains 101 keys to 110 keys.

  • Mouse is a small hand-held pointing input device used to enter data by pointing to a location on the computer monitor screen.

  • Trackball looks like an upside-down mouse and requires the ball to be rotated manually with a finger.

  • Joystick is a stick with its base attached to a flexible rubber sheath inside a plastic cover. It is used for playing video games.

  • Digitizing tablet has a flat bed tablet, and a pen with an electronic head which is moved on the tablet. Digitizing tablet is used for computer aided design of buildings, maps, etc.

  • Light pen contains a photocell in a small tube and is used to select objects directly on the computer screen.

  • Touch screen is a clear glass panel that is placed over the view area of the computer screen. The user uses the fingertip on the computer screen to select an option. It is used in ATMs.

  • Audio input devices use a microphone to input a person’s voice, a sound card to translate analog audio signals from microphone into digital codes and speech recognition to translate spoken words into text.

  • Video input is provided using video camera and digital camera. Computer vision is an area of computer science that deals with images.

  • Scanner is used to input data directly into the computer from the source document without copying and typing the data. A scanner can be a hand-held scanner or flat bed scanner.

  • OCR is a technique for the scanning of a printed page, translating it, and then using the OCR software to recognize the image as ASCII text that is editable.

  • MICR is used in banks to process large volumes of cheques. It is used to recognize the magnetic encoding numbers printed at the bottom of a cheque.

  • OMR uses an optical mark reader to detect marks on a paper. OMR is widely used to read answers of objective type tests, questionnaires, etc.

  • Barcodes are adjacent vertical lines of different width that are machine readable. Barcode reader reads the barcode. They are used to read labels in departmental stores and in libraries.

  • Printer prints the output onto a paper. Plotter is used for drawing maps, blueprints of ships, buildings, etc.

  • Impact printers are those in which the typeface strikes against the paper. Dot matrix printers, daisy wheel printers and drum printers are examples of impact printers.

  • Non-Impact printers do not hit or impact a ribbon to print. Ink-jet printers and laser printers are non-impact printers.

  • COM is a high-speed and low-cost process to record computer output directly from the computer tape on a microfilm. It is used to store manuals and for archiving of records.

  • Monitor is attached to the computer on which the output is displayed. The clarity of image on the computer screen depends on the resolution of screen, the dot pitch, and the refresh rate.

  • Screen image projectors display information from the computer onto a large white screen.

  • Audio output device like speakers, headset or headphone are used to output sound from the computer system.

  • I/O ports connect the I/O devices to the computer. Serial and parallel ports, USB port and Firewire are some of the commonly used I/O ports.

  • I/O system uses the I/O hardware (buses, ports, device controllers and I/O devices) and the I/O software (device drivers) for its working.


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