Output device is one which reveals results to outside world.
It accept the results produced by the computer the which are in coded form and
hence can not be easily understood by us and it convert these coded results to
human acceptable form. It supplies the converted results to the outside world.
Output devices can be classified in two types:
1. Soft copy
Output Device
2. Hard copy
device
Soft Copy Devices: This comes in category when power is
switched off, information are lost. Information is display till power is on.
Monitor: A monitor displays information in visual form,
using text and graphics. The portion of the monitor that displays the
information is called the screen. Like a television screen, a computer screen
can show still or moving pictures.
There are two basic types of monitors: CRT (cathode ray
tube) monitors and LCD (liquid crystal display) monitors. Both types produce
sharp images, but LCD monitors have the advantage of being much thinner and
lighter. CRT monitors, however, are generally more affordable.
VDU (Visual Display Unit): The computer screen is a display
device. A VDU can letters, symbols and graphics on its screen. VDU is popularly
known as a monitor. On monitor we can see the input information supplied to the
computer as well as the final result obtained after processing. Most VDU
monitor used a cathode ray tube that looks like a TV picture.
When the data input is fed through the keyboard of the
computer, electrical signals are generated. The CPU converts these signals into
alphanumeric or graphic display. So the output is obtained by optical display.
It contains about 20 to 49 rows of horizontal lines with each line divided into
80 spaces.
The screen is coated by phosphors.
Types of VDU:
MGA: MGA stands for Monochrome Graphics Adopter. The term
graphic is a since the device supports text only. The display device is with
single color i.e. black, black ground and white text. No graphics can be
achieved from this type of VDU.
CGA: CGA stands for Color Graphics Adopter. The CGA support
both text and graphics mode. Here the text has better resolution but the
graphics has a low resolution.
VGA: VGA stands for Video Graphics Adopter. This is very
nice representation of text and better graphic resolution. It supports 256
colors which is mixture of red, blue, green.
SVGA: It stands for super Video Graphic Adopter. This is an
advanced version of VGA. It has very nice color capability and can generate
million of color.
Hard copy devices:
These are those devices in which output
remains permanently. Hard copy can output devices are also called peripheral
devices because these are used as additional devices and are not compulsory
part of computer system. This is divided in two categories:
Printer: A printer transfers data from a computer onto
paper. You don't need a printer to use your computer, but having one allows you
to print e mail, cards, invitations, anouncements, and other materials. Many
people also like being able to print their own photos at home. Printers are the
most commonly used for output device that can be found in almost all computer
centres. These are the primary output used to prepare permanent document in
human readable form. There are two types of printer.
Impact Printer: The working of an impact Printer is exactly
similar to typewriter. The impact of a hammer against the ribbon squeezes ink
on to the paper. It is classified as:
Line Printer: A line Printer produces line at a time of
printed output. Line Printer are impact Printer used with most medium and large
computer system for producing high volume paper output. A line Printer is a
very fast output device the speed of Printer is from 300 to 25000 lines per
minute. it is classified in to two category:
Drum Printer:
A drum printer has a cylindrical drum having
the various characters embossed on its surface. The surface of drum is divided
into numbers of tracks. Total of track are equal to size of paper i.e. for a
paper width of 132 characters. Drum will have 132 tracks. There are 132
characters are printed in one line. The Printer is printed by striking a hammer
against the embossed characters drum is rotated at a high speed. The drum
printer is costly and complete needs replacement even if one character is
spoiled the speed of drum Printer is 300 to 2000 lines per minute.
Chain Printer:
This is the Printer in which characters are
embossed on a chain. They use a rapidly moving chain called a print chain. Each
link of the chain is a character font. They can bethought of as a tape wound on
two spools with a character set repeated three or four times. It also used
hammers to print characters. In order to enhance the speed of the chain
printers, the character set is repeated several times on the chain Character
printer. The speed chain printer is 400 to 3000 lines per minute.
Character printer:
A Character printer produces Character at
a time of printed output. The print head moves across the page, line by line
printing one Character at a time. These are the bidirectional printer i.e.
printer can print in either direction forward as well as backward. Character
printer can be divided in three category:
Letter Quality printer:
These printer use a print wheel font
known as a daisy wheel. Each petal of the daisy wheel has a character embossed
on it. A motor spins the wheel at a rapid rate. When the desire character spins
to the correct position a print hammer strikes it to produce to the output thus
daisy wheel printer are impact printer. Their output resembles a typed output
and they are noted for their print quality. The speed of these letter quality
printers normally ranges from 10 to50 character per second.
Dot Matrix printer:
The printers print each character as a
pattern of dots the print head. Compromise a matrix of tiny needles, typically
seven rows with nine needles. In (9X7 matrix) which hammer out the characters
in the form of pattern of tiny dots. The shape of each character i.e. the dot
pattern is obtained from information held electronically in the printer.
Ink Jet printer:
These are non impact printer based on a
relative new technology. They print character by spraying small drops of ink
onto paper. Special type of ink having high iron content is used. Droplets of
ink after laving nozzle. The droplets are then guided to the proper position on
the paper by electrically charged deflection plates. Ink Jet printer produce
high quality output because the characters are formed by dozens of tiny ink
dots. Moreover they are quiet and can form any kind of character. The document
printed may contain multiple character styles and a variety of type size.
Non impact printer:
Page printer: these are very high speed
non impact printer which can produce documents at a speed of over 20000 lines
per minute. Electronics, xerography, laser and technology have made these high
volume systems possible. These techniques called electro photo graphic
techniques have developed from the paper copier technology. Page printer can
produce pages of output at a rate equal to a paper copier. Each page produced
on these printers are original one since there are no carbon copy because of
their high cost, these printer are economical only when 100 of 1000 pages are
to be printed each month. Laser printer is the example of page printer.
Ink jet printers (non-impact printer)
• Use drops
of magnetic ink to produce dots on a page to produce text or images.
• The print
quality is almost the same as a laser printer's.
• Problems
with the ink
• The ink
is very expensive
• The ink
is water soluble and will run if the paper gets wet
• Highest
cost per page of all the printers
• For
producing color documents, it has the highest quality at a reasonable price.
Laser printers (non-impact printer)
How the laser printer produces an image
A laser or LEDs make dots on a light sensitive drum
Toner (very tiny particles of plastic) stick to the drum
where the dots where made
• Paper is
pressed against the drum and the toner is placed on the paper
• The paper
is heated and the toner melts into the paper
• Produces
the highest quality printout
• For black
and white printouts, very low cost per page
• Printout
is permanent
Plotters:
A plotter is an output device used to produce hard
copies of graphs and design hard copies of graphs and designs plotters are of
two types:
Drum Plotter:
In case of drum Plotter the paper on which the
design has to be made is placed over a drum that rotates back and forth to
produce vertical motion. The mechanism also consists of one or more pen holders
mounted horizontal across the drum. The pen(s) clamped in the holder(s) can
move to produce horizontal motion. Under the control of the pen(s) move
simultaneously to produce the deign and graphics. Since each pen is program
selectable pen having ink of different color can be mounted in different
holders to produce multi-colored designs.
Flat bed Plotter:
As the name implies flatbed plots on paper
that are spread and fixed over a rectangular flatbed table. In this type
normally the paper does not move and the pen holding mechanism is designed to
provide all the motion. Here also provision is there to mount more than one pen
in the pen(s) holding mechanism. Normally pens with ink of different colors are
used plotting. The plot size is restricted by the area of the bed. Some may be
a small and a some are large.
Plotters are normally slow in motion because of exercise
mechanical movement required during plotting. Hence there is great mismatch
between the speed of the CPU and the speed of Plotter because of this reason in
most cases output is first transferred by the CPU on to a tape is activated to
plot the design from the information on the tape. However in case of a computer
system dedicated to design work the CPU may send output directly to a Plotter.
Speakers:
Speakers are used to play sound. They may be built into the
system unit or connected with cables. Speakers allow you to listen to music and
hear sound effects from your computer.
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