Output Devices or Output Unit
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A computer has a wide range of output devices. It helps us to see what computer is doing. Without output units or device computer can input data, process it but could not produce output result. By using output device computer can produce result in the devices. A display unit is classified as an output unit as it displays results of computation. Mostly there are three common devices used to output data from a computer. There are Monitors or Display units, E-link display, and printers. Flat panel Display are used in display unit, e-ink displays (also called e-book readers) are recent and used to link download e-books (i.e., computer readable books). Printers are called hard copy devices as the data is written on paper and can be conveniently read by people without using any special gadgets. There are another set of output devices known as soft copy devices which store data in bit strings. They can be read and interpreted only by computers. Solid state memory sticks (called pen drives) are soft copy devices. As these are removable portable devices, the data in them can be read by another computer and stored it’s in memory for processing and produce output result in the screen. The most common human-understandable forms typically include text, visual, audio, or a hard copy (printed on a paper).
These output units or output devices are follows.
The
Examples of Output Devices:-
1. Monitor
· CRT Monitor
· LCD Monitor
· LED Monitor
· Plasma Monitor
2. Printer
A. Impact printers
a. Character Printers
Ø Dot Matrix Printers
Ø Daisy Wheel printers
b. Line printer
Ø Drum printers
Ø Chain printers
B. Non-impact printers
1) laser printers
2) inkjet printers
3. Projector
4. Plotter
5. E-link display
6. Speakers
7. Headphones
8. Sound card
9. Video card
10. GPS(Global Positioning System)
11. Braille reader
12. Speech Generating Devices (SGD)
1) Monitors:
-
A display unit also
known as a monitor.
· CRT Monitors :-
 |
| A CRT Monitor |
Till a few years ago, the technology used for most display units or Monitors were CRT Monitors or Cathode Ray Tube Monitor. They are now hardly used as they are bulky and consume too much power.
·
LCD Monitors:- Currently, the most technology used in Liquid Crystal Displays(LCD Monitors) which is als 
  LCD Monitor  The main principle used by Liquid crystal Display is the
polarizing property of light. A vertically polarized light beam is blocked by a
horizontal orientation to vertical orientation, the intensity of the light
emerging from the filter gradually increases. The rotation of polarizing filter
is mimicked by the rotation of liquid crystal display in LCD.   The main principle used by Liquid crystal Display is the
polarizing property of light. A vertically polarized light beam is blocked by a
horizontal orientation to vertical orientation, the intensity of the light
emerging from the filter gradually increases. The rotation of polarizing filter
is mimicked by the rotation of liquid crystal display in LCD.    The LED monitor is an improved version of the LCD monitor. Unlike
LCDs, LED monitors
·
Plasma Monitor:-  Plasma monitors use plasma display technology. These displays
usually consist of small cells between two glass panels. Cells typically
contain a mixture of noble gases with small amounts of mercury. When the
voltage is applied, the gas in the cells converts to plasma and emits
ultraviolet light to produce images on the screen. The plasma monitor is also a flat
panel display that is based on plasma display technology. It has small tiny cells between two glass panels.
These cells contain mixtures of noble gases and a small amount of mercury. When voltage is applied, the
gas in the cells turns into a plasma and emits ultraviolet light that creates images on the screen,
i.e., the screen is illuminated by a tiny bit of plasma, a charged gas. Plasma displays are brighter than
liquid crystal displays (LCD) and also offer a wide viewing angle than an LCD. 2) Printers:-
A printer produces hard copies of the Processes data. It enables the users, to print images, text or any other information onto the paper. Based on the printing mechanism, the printers are of two types:
Impact Printers and Non-impact
 Impact Printer These are Two Types:- A. Character Printers A.
Character Printers:-   Character printer prints a single character at a time or with a
single stroke of the print head or
·
Dot Matrix
Printers:-  Dot-matrix printers are contact printers. They are also called
serial printers as they print one character at a time with a printer head
moving across a line. The print head of a dot matrix printer consists of a set
of 9-24 pins arranged vertically. Dot matrix printers with 24 pins give a good
appearance to printed output and are quality printers. The ASCII code of a
character to be printed is sent to the printer electronics. The character code
is decoded by the printer electronics which selects a subset of pins on the
head to hit a carbon ribbon are successively selected to form a character which
is printed. Many dot matrix printers are bidirectional, that is, they print
from left to right as well as from right to left when the head returns. This is
possible as a buffer stores several lines to be printed. Printing in both
directions speeds up printing. The print electronics of dot matrix printers can
be modified to print scripts other than English, for example, Devanagari, Tamil,
etc. The reduction of cost of inkjet printers and their better print quality as
compared to dot matrix printers have considerably reduced the use of dot matrix
printers. However, dot matrix printers are still used to create multiple copies
of a document. Further, the recurring cost of printing is low (about a tenth of
the cost of an inkjet printer). As dot matrix printers are contact printers, it is easy to obtain
multiple copies by placing carbon sheets between paper sheets. Continuous
stationery, that is , fan-fold forms with holes on both sides which are
advanced by sprockets on both ends of the printer’s carriage are usually used
in these printers. However, Single sheets of paper of variable width up to 13.5
inches may also be used. Paper quality may be poorer than the ones used in
Inkjet/laser printers. As the cost of
consumably (namely, printer ribbon, paper) is low and print and graphics
quality are adequate for most office use, they are preferred by small business
and government offices. One of their primary disadvantage is that they are
noisy compared to inkjet and laser printers and may disturb co-workers in
shared offices.
·
Advantages
·
Disadvantages B. Daisy Wheel
printers:-  Daisy Wheel Printer was invented by David S. Lee at Diablo Data Systems.
It consists of a wheel or disk Advantages A.
Line Printers:-A line printer prints a complete line at a time. Printing speed varies from 200 to 2000 lines per minute with 75-300 characters on a 15 inch line. Six to eight lines per vertical per vertical inch are printed. Printers are available in almost all scripts, for example, Japanese, Arabic, Cyrilic (Russian), Hindi, Tamil, Telegu, etc. Early line printers were of two types called drum printers and chain printers.
Drum printers:-  Drum Printer Drum printers are line printers, which prints one line at a time. Drum printers consisted of a cylindrical drum on whose surface sets of character to be printed were embossed. Drum Printers are impact printers, because they print by hammering the paper and the inked ribbon against the character on the drum. Hence, they can be used to produce multiple copies by using carbon paper or its equivalent. However, due to impact printing, drum printers are noisy in operation, and often use a cover to reduce the noise level. Typical speed of drum printers is in the range of 300 to 2000 lines per minute. ·
Chain/Band Printers:-     Chain/Band printers are line printers, which print one line at a time. The print mechanism of a chain/band printer consists of a metallic chain/ band on which all the characters on which all the character set supported by the printer are embossed. A standard character set may have 48, 64, or 96 characters. In order to enhance the printing speed, the characters in the character set are embossed several times on the chain/band. For example, the chain/band of a 64 character set printer may have 4 sets of 64 characters each embossed on it. In this case, the chain/band will have altogether 256 (64*4) characters embossed on it. In addition to the chain/band, the printer has a set of hammers mounted in front the chain/band in a manner that an inked ribbon and paper can be placed between the hammers and the chain/band. The total number of hammers is equal to the total number of print positions. If there are 132 print position, the printer will have 132 hammers. The Chain/band rotates at a high speed, and a character at a print position is printed by activating the appropriate hammer, where when the character embossed on the chain/band passes below it. Since the character set is repeated several times on the chain/band, it is not necessary to wait for the chain/band to make a complete revolutionary to position the desired character in the current position. Unlike drum printer, the chain/band printer can be easily changed. This allows the use of different fonts and different scripts to be used with the same printer. Just like drum printer chain/band printers can only print predefined xset of characters, which are embossed on the chain/band used
with the printer. Due to the chain/ band pictures do not have the ability to
print any shape of characters, different size of print, graphics, such as
charts and graphs.
Chain/band pictures are impact printers, they print by hammering the paper and the linked ribbon against the characters embossed on the chain/band. Hence, they can be used multiple copies by using carbon paper or its equivalent. Due to impact printing, chain/band printers are noisy in operation, and often use a cover to reduce the noise level. Typical speeds of chain/band printers are in the range 400 to 3000 lines per minute. Non-Impact Printer:- a)
Laser Printers:-   Laser Printers are faster than inkjet printers. Low-Cost printers
prints eight pages per minutes and have become affordable even for home use.
They have a resolution of 600-1200 dots per inch, depending on the cost of the
printer. The printer prints dots based 0s and 1s in the bit mapped image to be
printed. The steps followed to print a page are: 1. The bit mapped image of a page stored in the printer’s memory
is scanned horizontally from left to right line by line. 2. A laser beam is reflected by a mirror system and moves from
left to right along a horizontal line. The reflected beam impinges on the
surface of an electricity sensitive cylinder. 3. When a 1 is encountered in the bit map, it turns on the laser
beam. Else it is turned off. 4. The dot where the laser beam hits the surface of the cylinder
is changed. If there are 600 bits perline, 600 dots are created on a line of
the cylinder. 5. The cylinder rotates near a reservoir containing a toner. The
toner is attracted to the changed spots on the cylinder and adheres to these
spots. 6. A paper is placed bellow the roller. It is transported across
the cylinder as the cylinder rotates. 7. The paper is pressed between the cylinder and a rigid heated
pate. The toner sticking to the cylinder is transferred to the paper as the
cylinder rotates. The image is transferred to paper is sharp and of high quality as
the laser beam is very sharply focused and the spot on the cylinder is burred.
Laser printers of resolution 1200 bits/ inch are available commercially. Colour
laser printers are also available, but per page cost is double that of black
and white printers. Advantages a)
Inkjet Printers:-  An inkjet printer consists of a print head which has a number of
small holes or nozzles. Ink wells hold ink near the nozzles. Individual wells
can be heated very rapidly (in a few microseconds) by an integrated circuit
resistor. When the resistor heats up, the ink near it is ejected through the
nozzle and makes dots on paper placed near the head. A high resolution inkjet
printer has around 50 nozzles within a height of 7 mm and can print with a
resolution of 300 dots per inch. A fairly complex electronic system selects the
nozzles to be heated based on the character to be printed. The printer has
enough memory to print an entire page accommodating different fonts. The
characters printed on paper are fused in it by moving the paper between
rollers. Colour inkjet printers use
three separate inkjets, one for each colours, all colours are created. The
printing speed of inkjet printers is around 120 characters per second. Pictures
can be drawn with inkjet printers besides printing text by storing the bit map
of the image in the printer’s memory. Inkjet printers are inexpensive. The
print cartridges are expensive. They may cost almost half the piece of the
printer. The cheaper the printer, the more expensive is the cost of the
replacement cartridge. Thus, when you buy an inkjet printer, it is wise to ask
the cost of a replacement cartridge. Advantages 3)
Projector:- A projector is an output device that enables the user to project
the output onto a large surface such A projector is a display output device because it receives images
from a computer and transfers Previously, projectors used lens
systems that produced images by shining light through transparent lenses.
Modern projectors use laser systems to directly project images using lasers. Modern
projectors are also called video projectors because these projectors can also
project moving images along with still images.
Liquid
Crystal Display (LCD) digital projector:  These types of digital projectors are very popular as they are
lightweight and provide crisp output. An LCD projector uses transmissive
technology to produce output. It allows the light source, which is a standard
lamp, to pass through the three colored liquid crystal light panels. Some
colors pass through the panels and some are blocked by the panels and thus
images are on the screen. Digital
Light Processing (DLP) digital projector:-  It has a
set of tiny mirrors, a separate mirror for each pixel of the image and thus provides
high-quality images. These projectors are mostly used in theatres as they
fulfill the requirement of high-quality video output.
In simple words, an output device is a type of peripheral device
that helps us to get data 4) Plotters:-Even though printers can be used to draw figures, they are
not suitable to draw engineering drawings, such as building plans, machine
parts, circuit diagrams, etc. Thus, special plotters to produce good quality
drawings have been designed and are available in the market. There are two
types of plotters. One is called a drum
plotter and the other a flatbed
plotter.
I.
Drum Plotter:-   In a drum plotter, the paper on which the graph is to be drawn is mounted on a rotating drum. A pen which can move linearly, that is, perpendicular to the direction if drum rotation, is mounted on a carriage. The drum can rotate in clockwise or anticlockwise direction under the control of the plotting instructions sent by the computer. The pen can move left to right or right to left. The pen can also move up and down. The movements of the pen and drum are controlled by graph plotting program. The program can thus draw various drawings and also annotate them by using the pen to draw characters. I. Flatbed Plotter:-   A flatbed plotter has a stationary horizontal plotting surface on which paper is fixed. The pen is mounted on a carriage which can move in X or Y direction. The pen can also be moved up or down. A graph plotting computer program is used to move the pen to trace the desired drawing. A plotter is an output device that is almost identical to a
printer. However, it is primarily used to print vector graphics with high
quality. Unlike a printer, a plotter has various advanced features and can also
print on cardboard, film, fabric, and many other synthetic surfaces. The plotter
helps to produce large-size hard copies of graphics or designs. It derives the
design from the graphic card and then interprets the vector graphics. A plotter
usually uses color pens to draw multiple lines between different points to
create the entire design. Plotters are expensive compared to printers. 5) E-ink
display:-      E-ink display is primarily used to display e-books. This display’s main advantage is that it does not consume any power while it displays a page. Only when a new page is to be displayed (i.e., when a page is flipped to a new page), power is consumed. Another advantage is easy readability in bright light. Its reading comfort is almost as that of printed paper. LCDs, on the other hand, strain the eyes of the reading comfort is comfort is almost as that of printed paper. LCDs, on the other hand, strain the eyes of the reader as the screen is refreshed 60 times a second and this affects reading comfort. LCDs are also difficult to read in bright light as they are lit by a light source whose power is limited. E-ink consists of millions of transparent micro-capsules which encapsulate electrically charged black and white pigment balls. These micro-capsules are sandwiched between a transparent electrode layer which has a grid of electrodes and a supporting layer. When a positive voltage is applied to the electrode layer, the black pigment balls which are negatively charged migrate upwards in the bubble and black dots are seen. A negative voltage applied to the electrode brings the white balls to the top. The grid of electrodes is used to address the capsules and create black and white pixels which make up a text or a picture. The bubble reflects ambient light. Thus, the display can be read wherever there is adequate light, including bright sunlight. The bubbles remain undisturbed until the voltages applied to the grid of electrodes are changed. Thus once a page of text is displayed, there is no consumption of power. Power is required only when bubbles are to be rearranged to display another page. In the e-book application, this is a great advantage as power is consumed only when pages are flipped by a reader. Thus, once the rechargeable batteries of an e-book are charged, it need not be recharged for a few days. Currently, e-mail is primarily black and white. Colour e-ink readers are now available but are expensive. Animation is also not possible in e-books, as the response time of bubbles is slow. E-ink technology is still evolving and is currently being used primarily in e-book readers. It is expected that foldable e-ink displays will appear. Currently, three popular e-book readers are Kindle marketed by Amazon. Nook marketed by Barnes and Noble and Sony Reader. Typical e-book readers are light (around 300g), easy to hold in the hand (19cm * 13.5 cm) and with (600*800) pixel display. Books are downloaded to the using Wifi or mobile telecommunication System. They can incorporate text to speech convertors and music players. Wikipedia for e-ink or how the stuff works e-link. Wikipedia for e-link or how the stuff works e-link. Wikipedia also has full specifications of the latest e-book readers marketed by several companies. 6) Speakers:- Speakers are one of the most common output devices used on computers to achieve audio output. Computer speakers usually receive signals from the sound card and then convert them to audio. These speakers use internal amplifiers that vibrate at different frequencies to increase/decrease the volume or amplitude of the sound as per the choice of the user.   Most monitors and laptops come with inbuilt speakers.
However, we can also connect external speakers to the computer via both wired
and wirelessly. The speakers are mainly used to obtain the loud sound output. 7)
Headphones:-
Headphones,
also known as earphones, are output devices that allow us to listen to audio
from a |
