OUTPUT DEVICE

It is a machine which provides communication of information from machine to man. Output units are just inverse manner of input units. We feed data into computer by typing on the keyboard of computer. Similarly information coming out of computer can be typed on the sheet of paper by an output unit known as printer. The output coming from the CPU is in the form of electronic binary signals which needs conversion in the same form which can be easily understood by human beings i.e. graphical, alphanumeric in human language, audio visual. This function is performed by Output units.

Output can be given:

  • On the screen by visual display unit
  • In printed form by printers
  • In graphic form by plotters
  • In audible sound form by speech synthesizers
  • Through other output units.

Output devices may adopt different shapes and styles. The output may be in form of typed, printed or sketched matter or may be visible or audio type. But we can broadly classify them as

  • Hard Copy Device
  • Soft Copy Device

By hard copy we mean output in direct usable form that is in printed or plotted form. Whereas Soft -copy is in magnetic/audible form that cannot be used directly. Hard-copy devices produce a permanent record on media such as paper sheets or paper tape. Soft-copy devices do not produce a permanent record, but some soft-copy devices incorporate a printer for hard copy. Hard copy devices are very slow in operation as compared to soft copy devices.

PRINTER

Printers are used for producing output of information on a paper. There are different variety of printing devices which is classified according to the print quality and the printing speeds.

Personal computers printer can be divided into two categories:

  • Impact
  • Non-impact

Impact printers

Impact printers use variations of standards typewriter printing mechanism where a hammer strikes paper through inked ribbon and create impression on the paper. These printers are of two types-

  1. Character printers
  2. Line printers

Character Printers

Character printers are the printers which print one character at a time.

These are further divided into two types:

  1. Dot Matrix Printer(DMP)
  2. Daisy Wheel
  1. Dot Matrix
    2. A printer that produces graphics and text by printing dots onto the page much like the way your screen displays output by combining small dots together. In a dot-matrix printer, individual characters are formed by needles which are selectivity hit against the inked ribbon to the paper, forming patterns composed of small dots. Dot matrix printer speeds usually range between 30 and 600 cps. The printing head contains a vertical array of pins. As the head moves across the paper, selected pins “fire” against an inked ribbon to form a pattern of dots on the paper.
  2. Daisy Wheel

    3. It is an impact printer is so named because the print heads resemble a daisy flower, with the printing arms appearing like the petals of the flower. All the Characters are embossed with a metal. The daisy wheel mounted on carriage, which can move from, left to right and back and can also rotate. The embossed characters strike the ribbon and impression is made on the paper mounted behind the ribbon.

Line printer


Line printers are the printers which print one line at a time. These are of further two types -
  1. Drum Printer

    2. This printer is like a drum in shape so it is called drum printer. The surface of drum is divided into number of tracks. Total tracks are equal to size of paper i.e. for a paper width of 132 characters, drum will have 132 tracks. A character set is embossed on track. The different character sets available in the market are 48 character set, 64 and 96 characters set. One rotation of drum prints one line. Drum printers are fast in speed and can print 300 to 2000 lines per minute.

  2. Chain printer

    3. In this printer, chain of character sets are used so it is called Chain Printer. A standard character set may have 48, 64, or 96 characters.

Non-Impact Printers

Non-impact Printers uses chemical, heat or electrical signals to etch or induce symbols on paper. Many of these require special coated or treated paper.

  1. Leaser

    2. This is a high quality, high speed, high volume technology which works in non-impact fashion on plain paper or pre-printed forms. Printing is achieved by deflecting laser beam on to the photo sensitive surface of a drum and the latent image attracts the toner to the image areas. The toner is then electrostatically transferred to the paper and fixed into a permanent image. Speeds can range from 10 pages a minute to about 200 pages per minute. This technology is relatively expensive but is becoming very popular because of the quality, speed and noiseless operations.

  2. Ink Jet

    3. This printer is Non-Impact categories and it is known as bubble jet printers they print by spraying a controlled stream of tiny ink droplets accurately on the paper forming either dot matrix or solid characters. It is high-quality, low cost and speed range from 50 cps to above 300 cps. This technology has been used well for production of colour printing and elaborate graphics.

  3. PLOTTERS

    4. Plotter, for instances will draw you a graph or map out the world by tapping pens up and down on a sheet of paper until every patch is appropriately coloured.

MONITOR:


It is the most essential part of the computer and also known as Visual Display Unit (VDU). The monitor provides a window through which the user can see the program and output information. Graphic display is made up of a series of dots called ‘pixels’ (picture elements) whose pattern produces the image.

A display is a computer output surface and projecting mechanism that shows text and often graphic images to the computer user, using a cathode ray tube (CRT), liquid crystal display (LCD), light-emitting diode, gas plasma, or other image projection technology. Displays for personal computers have steadily improved since the days of the monochrome monitors that were used in word processors and text-based computer systems in the 1970s.

In 1981, IBM introduced the Color Graphics Adapter (CGA). This display system was capable of rendering four colors, and had a maximum resolution of 320 pixels horizontally by 200 pixels vertically.

In 1984, IBM introduced the Enhanced Graphics Adapter (EGA) display. It allowed up to 16 different colors and improved the resolution to 640 pixels horizontally by 350 pixels vertically. This improved the appearance of the display and it possible to read text more easily than with CGA. EGA did not offer sufficient image resolution for high-level applications such as graphic design and desktop publishing.

In 1987, IBM introduced the Video Graphics Array (VGA) display system. This display support high resolution application. Its resolution depends upon the numbers of color used. You can choose between 16 colors at 640 X 480 pixels, or 256 colors at 320 X 200 pixels. In 1990, IBM introduced the Extended Graphics Array (XGA) display. A later version, XGA-2 offers 800 by 600 pixels resolution in true color (16 million colors) and 1,024 by 768 resolution in 65,536 colors.

After 1999, IBM introduced the Super Video Graphics Array (SVGA) displays. It offers palette of up to 16,000,000 colors and small SVGA display 800 by 600 pixels and large monitor ( above 20 inches) can display 1280 X 1024 or even 1600 X 1200, pixels.