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By Jide Awe | Contributing Writer
OUTPUT DEVICES
Another introductory
topic is that of output devices such as a monitor, printer or plotter.
(i) PLOTTER
A plotter is a
device which uses a motor to move pens or drawing implements in tightly
controlled horizontal and vertical motions on a piece of paper or
film. The computer can control a plotter to combine on one piece of
paper differing pen colors and text and pictures stored within the
computer. Computer plotter can be purchased with flat table or flat
bed configurations or in models which move the pen(s) back and forth
with gears that also drive the paper movement at the same time.
(ii) PRINTER
The printer is
probably the most common and useful output device attached to your
computer. There are many types of modern computer printer with differing
speeds and capabilities. The most common printer is the Dot matrix printer which provides characters made up from tiny dots of
ink on paper. Line printers (usually with Mainframe computers or Minicomputers)
print entire lines of text in one sweep then move to the next line
and are thus very fast. Ink jet printers produce characters made from
individual dots of ink sprayed onto the paper.
The ink jet printer squirts individual dots of ink onto the paper
to form letters or other characters. A high quality paper is necessary
since the wet ink can smear if not carefully handled. Although with
the most recent models, ordinary paper can also be used. The Colour
print facility is also now standard with most inkjet printer.
Finally, laser printers use a rapidly scanning laser to sensitize
a polished drum with an entire page of information quickly and look
and work roughly like an office copier. The first two printers are
classified as impact printers since something strikes the paper while
the later two are non impact printers.
The laser and
ink jet printers are becoming more popular due to rapid speed of printing
and quiet mode of operation.
The laser printer is used for quickly producing one page of text at
a time. In operation, the laser scans a polished drum with an image
which is then dusted with dark toner particles which stick to the
exposed areas made sensitive by the laser. Paper is then placed in
contact with the drum and the toner is transferred to the page and
is finally fused with heat to "fix" or seal the toner particles
to the page. Of the Microcomputer printers, the Laser is the most expensive in
terms of purchase price, maintenance cost and consumable cost.
Dot matrix printers
are common and affordable alternatives for many small offices, home
computer hobbyists or organizations with voluminous printing requirements
(e.g. statements of accounts for banks). The Dot matrix is additionally
designed for use with continuous flow paper, as well as typical single
sheet paper.
Dot matrix usually operates in varying modes of draft and letter quality.
In draft mode, the printer speed is faster, with draft quality. Letter
quality is slower with higher quality.
Dot matrix printers produce letters via small pins which strike the
ink ribbon and paper to produce print which can be jagged looking.
Nine pin dot matrix printers produce somewhat rough looking letters
while 24 pin dot matrix printers produce crisper, fully-formed letters.
The Dot matrix printer strikes the paper through a ribbon to transfer
ink to the printed page.
Connecting a printer
via a cable to the computer is always done through one of two plugs
(or interfaces) on the back of the computer. One type of interface
(computer plug) is serial, the other called parallel.
The most commonly used interface for printers today is the parallel
interface but serial interface printers do exist. What is the difference?
Recall that there are eight bits (computer dots and dashes) to a byte
(or computer word). The serial interface has each bit sent one at
a time to the printer - like men in single file at the supermarket
checkout counter. The parallel interface sends all eight bits at once
- like eight men all entering eight supermarket counters at once.
Each interface is different, the printer manufacturer will tell you
which interface to use, i.e. serial or parallel. Frequently, modems or mouse devices use the serial interface leaving
the printer to the parallel interface.
(iii) MONITORS
We have talked
about output to paper, next let's briefly discuss output to a monitor
or screen. The monitor is a television like device that the computer
uses to communicate with you. The monitor or video display works much
like your television - some older home computers still use a TV. An
old term for a monitor is the cathode ray tube or CRT. Monitors differ
in the sharpness or resolution they can display. On the low end of
the resolution spectrum is the monochrome (single color) monitor frequently
available in either green or amber screens. Next is the color RGB
monitor (RGB stands for Red, Green and Blue) which displays low resolution
color dots to make up an image.
Higher resolution is obtained with an EGA monitor (Enhanced Graphics
Adapter) and still higher with a VGA (Video Graphics Array) Monitor
and even higher with an SVGA (Super Video Graphics Array) Monitor.
Each monitor is matched to work with a circuit card located within
the body of the computer. One way to upgrade a computer is to switch
both the monitor and display/graphics circuit card to produce a sharper,
more colorful image. The dots which make up all images on the monitor
screen are called pixels. The smaller the pixels, the higher and sharper
the image resolution.
Typically the monitor displays 80 columns (characters) by 25 rows
(lines) of information. The initial SVGA cards could only display
16 colours. And then 256 colours. Now some SVGA card can display millions
of colours.
INPUT &
OUTPUT DEVICES
Certain devices can act as both input and output devices to the computer.
Typical devices mentioned earlier are the disks (floppy and hard).
(i) MODEM
Short for Modulator/Demodulator.
A device to send and receive computer output over telephone lines.
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