Output device
displays result of the computer processing for user. The popular output devices
are monitor, printer and speaker (audio response systems).
1. Visual
Display Unit or Monitor
Visual display
units (VDUs) are television-like screens that provide the user-interface in the
form of display of text, numbers and images. The VDUs may be monochrome or
colour. The support of monochrome or colour and clarity of display depend on
the type of video monitor and the video adapter installed in the microcomputer.
The video
display terminal (VDT) consists of a monitor or CRT and a keyboard. The CRT
serves as an output device and the keyboard as an input device. Thus VDT is
an input/output device. If the terminal is provided with some memory and certain
processing capability, it becomes a smart or intelligent terminal. A terminal
without processing power is called a dumb terminal.
2. Speaker
and Audio Response Systems
Computer can
produce verbal output where the output or response can be standardized as
replies to special requests for information. The unit analyses the input and
delivers the verbal reply by assembling the responses from pre-recorded words
and phrases.
3. Printers
Printers are
purely output devices. They produce hard copy output. Computer printers vary
widely in their technologies and capabilities. They can be classified in a
number of ways. First, they can be classified into three broad groups:
character printers, line printers and page printers.
They can also
be classified into impact and non-impact printers based on the basis of the
printing mechanism.
The impact
printing technology uses some mechanical pressure to produce images on
paper. The impact printers include dot matrix printer, daisy wheel printer and
chain printer. It is possible to
take multiple
copies of output with impact printers. Non-impact printers do not use
mechanical force to produce output on paper and hence they can produce only
single copy output. Thermal
printer, Inkjet
printer and laser printer are all non-impact printers. Of these several types
of printers, dot matrix printer, inkjet printer and laser printer are very
poplar.
3.1 Dot
Matrix Printer (DMP)
DMP prints one
character at a time as a set of dots produced by the pins on the print head. It
uses a nine or twenty-four pin print head. The pins or printing wires are
aligned into the shape of the character to be printed before the print head
strikes the ribbon. The impact of the strike produces character shapes on paper.
The speed of DMP is measured in character per second (CPS). A normal dot matrix
printer with nine or twenty-four pin print head can produce output ranging from
50 to 600 characters per second. It produces lot of noise when working. The
popular DMPs are Epson, Panasonic, Citizen, Wipro, TVSE and Lexmark. The
operating cost for DMP is the lowest among all types of printers.
3.2 Inkjet
Printer
Inkjet is a
non-impact printer and is quiet when working. It sprays ink particles through
its nozzle. On leaving the nozzle, the tiny particles of ink get electrically
charged. The electrically charged particles are then guided on to the paper to
form appropriate characters. Inkjet printers are as cheap as dot matrix printers
are; but their operating costs are far higher than those of dot matrix printers.
However, they give much better quality than DMPs. They are available in black
and white and colour. The popular brands of inkjet printers are
Hewlett-Packard, Epson Stylus and Canon.
3.3 Laser
Printer
Laser printer
is a high-end printer. It is more expensive than inkjet printers and its
operating costs are also higher than inkjet printers. It uses the same
technology as that of Xerox copier machines and it can produce both character
and graphic output. It gives the best quality output. Though expensive, laser printer
is becoming increasingly popular.
3.4 Daisy
Wheel Printer
The daisy wheel
printer has a wheel with a number of spokes made up of metal and plastic. Each
spoke carries a typeface at the outer end. The wheel rotates until the
appropriate character
comes under the
hammer, which strikes to produce the impression on paper. These wheels are
inexpensive and removable. It is slow and produces noise like dot matrix
printer; but it gives fine quality output.
3.5 Thermal
Printer
The thermal
printer generates heat to produce the required character shape on specially
coated thermal paper. The print head, which carries electric current, burns the
aluminium coating on the paper into the character form. It is a quiet printer.
3.6 Drum
Printer
It is a line printer.
It has a drum that rotates at high speed. A set of characters is embossed on
the drum. It prints one line of characters at a time. The hammer for a
particular character position is activated when that character on the drum
passes under it to produce character impression on paper.
3.7 Chain
Printer
'The chain
printer works like the drum printer. It consists of a set of typefaces on a
chain that rotates at high speed. The printer composes one line at a time and
the hammers are activated to produce one row of characters as it is composed. There
is a hammer for each print position. As the characters move around on the
chain, the hammer strikes on the opposite side of the print position to produce
character impression on paper.
3.8 Magnetic
Printer
In a magnetic
printer, a drum coated with magnetic material captures the image of the page to
be printed. These magnetic spots attract dry ink particles, which are then
pressurised and transferred to paper to produce output.
4. Graphic
Plotters
Plotters are used
for plotting graphs and designs on paper. Architects and designers use plotters
to produce blueprints of their designs on paper. It is a specialised output
device for preparing computer drawn charts and graphs. The most popular type of
plotter is the flat bed device. It plots on paper (or other material) that is
spread on a flat bed.
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