Computer Output Devices: At present, EL and gas-plasma technology are more expensive thus are not used as often as LCD technology.

Printers: printers are used to print characters, symbols, and graphics on paper. They are divided into two categories:

  1. Impact printers
  2. Non-impact printers

Impact printers Non-impact printers

Impact Printers: An impact printer forms characters or images by striking a mechanism such as a print hammer or wheel against an inked ribbon, leaving an image on the paper. Following are a few types of impact printers:


  • Dot-matrix printer: it contains a print head of small pins, which strike an inked ribbon against paper, forming characters or images. Print heads are available with 9, 18, or 24 pins, with the 24-pin head offer the best quality prints.
  • Daisy-wheel printer: this printer uses a mechanism is the shape of a series of petals arranged on a petal wheel., having a character at the end of each petal. A character comes into a print position by wheel rotation and an image is formed by the hammer strike on the desired character. It is slower than dot-matrix printer but better in quality.
  • Line printer: this type of printer is normally used by mainframe and minicomputers. It prints a whole line of characters at once rather than a single character at a time. Some of these can print up to 3000 lines per minute. It is of two types: chain printer and band printer.
  • Non-Impact Printers: Non-Impact printer forms characters or images without making direct physical contact between printing mechanism and paper. There are three types in this category.
  • Laser Printer: it is similar to a photocopying machine and it use the principle of dot-matrix printers of creating images with dots. These images are created on a drum, treated with a magnetically charged ink-like toner (powder), and then transferred from drum to paper. The laser printer can produce high quality images of both text and graphics (ranging from 300dpi to 1200 dpi). Its speed varies from 4-32 text-only pages per minute for microcomputers and up to 200 pages per minute for mainframes.
  • Ink-jet printer: ink-jet printer sprays small, electrically charged droplets of ink from four nozzles through holes in a matrix at high speed on to paper. It is cheaper compared to laser printer but lower in resolution (300-720 dpi) and is slower also (1-6) text-only pages per minute. It has another type of printer i.e. bubble-jet printer, which uses miniature heating elements to force specially formulated inks through print heads with 128 tiny nozzles.
  • Thermal Printer: thermal printer uses colored waxes and heat to produce images by burning dots on to special paper. The colored wax sheets are not required for black-and white output. It produces a high quality printout but is quite expensive compared to other non-impact printers.

Plotters: A plotter is used to produce high-quality graphics in many colors and used for specialized applications i.e. architectural drawings, maps, graphs, and charts. Plotters are of two basic kinds:

  • Flatbed Plotter
  • Drum plotter

Flatbed Plotter: a flatbedĀ  plotter is the one, which has a paper lying flat on a table-like surface. The bed-size varies according to the need. One to four color pens move across the paper and the images are printed by the computer accordingly.

Drum Plotter: it works like a flatbed plotter with a difference that the paper is mounted over a drum, enabling a continuous output. A typical usage is to track an earthquake readings.

Sound output: Speakers are most commonly used to have this type of output.

Speaker: as we use microphone to input audio data to the computer, conversely we use speaker to get audio output from the computer. It works on the same principles to convert sound data into machine sable form. A variety of speakers are available in the market to satisfy the requirements of the users.

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