Output Devices:
An output device is any device used to send data from a computer to another device or
user. Most computer data output that is meant for humans is in the form of audio or video.
Thus, most output devices used by humans are in these categories. Examples include
monitors, projectors, speakers, headphones and printers.
Hard Copy
Output that is in the form of print document, which can be read directly, long last and
permanently stored. E.g. A word document containing text and images printed by the
printer on a paper.
Soft Copy
Output that is in the form of metallic or audio form, which is cannot be read directly by the
user. E.g. A collection of music files and folders on a CD.
Accordingly the output devices are classified as hard copy devices and soft copy devices.
Hard Copy Devices : printers, fax machine, photographic output devices etc.
Soft Copy Devices : monitors, data projectors, speakers etc
Following are some of the important output devices used in a computer.
Monitors
Graphic Plotter
Printer
Monitors
Monitors, commonly called as Visual Display Unit (VDU), are the main output device of a
computer. It forms images from tiny dots, called pixels that are arranged in a rectangular
form. The sharpness of the image depends upon the number of pixels.
There are two kinds of viewing screen used for monitors.
Cathode-Ray Tube (CRT)
Flat-Panel Display
Cathode-Ray Tube (CRT) Monitor
The CRT display is made up of small picture elements called pixels. The smaller the pixels,
the better the image clarity or resolution. It takes more than one illuminated pixel to form
a whole character, such as the letter ‘e’ in the word help.
A finite number of characters can be displayed on a screen at once. The screen can be
divided into a series of character boxes - fixed location on the screen where a standard
character can be placed. Most screens are capable of displaying 80 characters of data
horizontally and 25 lines vertically.
There are some disadvantages of CRT −
Large in Size
High power consumption
Flat-Panel Display Monitor
The flat-panel display refers to a class of video devices that have reduced volume, weight
and power requirement in comparison to the CRT. You can hang them on walls or wear
them on your wrists. Current uses of flat-panel displays include calculators, video games,
monitors, laptop computer, and graphics display.
The flat-panel display is divided into two categories −
Emissive Displays − Emissive displays are devices that convert electrical energy into
light. For example, plasma panel and LED (Light-Emitting Diodes).
Non-Emissive Displays − Non-emissive displays use optical effects to convert sunlight or
light from some other source into graphics patterns. For example, LCD (Liquid-Crystal
Device).
LCD (Liquid crystal display) Monitor:
It produces a picture by passing polarized light from the surroundings or from an
internal light source through a liquid crystal material that can transfer light. It works on
the principle of blocking the light rather than emitting the light which enable them to
consume less power than CRT monitor. Liquid crystalline material is sandwiches between
two glass or plastic plates. The front plate is transparent and the back plate is reflective.
There is a coating of thin film on the front plate. The coating is transparent and conductive.
An electrically conductive film is put on the back plate. A voltage is applied between a
segment and the back plate to create an electric field.LCD doesn’t emit their own light.
LCD uses fluorescent lights.
LED (Light Emitting Diode) Monitor:
It is a flat panel display, which uses an array of light emitting diodes as a video
display. LED displays are actually the LCD displays with an LED backlight to power up the
LCD panel. It means that LEDs are placed behind or around the LCD panel to enhance the
luminosity. LED uses light emitting diode while LCD uses fluorescent lights. Printers
Printer is an output device, which is used to print information on paper.
There are basically two types of printer:
1. Impact printer.
2. Non-impact printer.
Impact printer: They are like type typewriters. The characters are formed by physical striking against inked ribbon. eg. Dot
Matrix, Daisy Wheel, Line printer (Drum printer, Chain printer).
Non-impact printer: It does not strike the paper to print the characters. These characters are formed by electrostatic, inkjet,
laser or heat technology.
Since, there is no physical contact between the printer and the paper, they have less number of moving parts and produce
low noise. They are faster than impact printers. There are normally three types of Non-impact printers:
a. Thermal printer: It uses heat to print.
b. Ink-Jet printer: It uses spray method to print.
c. Laser printer: It uses laser beam to print.
Note: Printer is classified in three categories, by how they print and how fast they operate:
i. Character printer: Such printer’s print one character of the text at a time.
ii. Line printer: Such printer prints one line of text at a time.
iii. Page printer: It prints one page of the text at a time.
Impact Printers:
A. DOT MATRIX:
Such type of printer uses the dot matrix printing mechanism which allows to print a character by printing the selected
number of dots from a matrix to form a matrix [ as rows and columns ] of dots .The dot matrix consists of dots of rows and
columns. It contains a print head of small pins that strikes on inked ribbon forming characters or images. Prints head are available
with 9, 18,24 pins. Printing speed lies in the range of 30-600 CPS( character per second).They are noisy.
B. DAISY WHEEL :
The print element of this printer is a flat spoke wheel with characters embossed along the outer edge of the spokes. They
daisy wheel print element rotates to the appropriate characters which is then struck with a hammer. It has speed of about 90 CPS
(character per second).It is noisy and it can’t print graphics.
LINE PRINTER:
This is a special type of impact printer which works like dot matrix printer but uses a special wide print head that can print
an entire line of text at one time. Line printer do not offer high resolutions but are fast. The fastest line printer can print 3000 lines
of text per minute.
Impact line printer is explained as follows:
a) Drum printer: It contains characters on a rotating drum. The hammer hit the paper and ribbon against the desired
characters on the drum when it comes in the printing position. Its noise level is high. Its speed varies from 200-2000 lines
per minute.
b) Chain printer: It contains character on rotating chain. They print one line at a time. When desired character comes in the
print position the hammer strikes the ribbon and paper against the character. Noise level is high. Its speed ranges from 400-
2400 lines per minute.
c) Band printer: They contain fast rotating steel print band in place of chain which is embossed with characters. Hammers
strike the ribbon and the paper against the character to print it. Some band printer up to 3000 lines per minute. In such
printer noise level is high.
Non-Impact printers:
I. INKJET PRINTER:
Inkjet printer create an image directly on the paper by spraying ink through tiny nozzles. Nozzles can hold four different
colours, CYMK ( Cyan( Blue-Green),Magenta (Purple red ),Yellow and black (K stands for black).Others colors are derived by
the combination of these four colours.It is quieter than dot matrix printer and produces high quality images. They are also called
bubble-jet printers. It work by forming an image that is composed of tiny dots, but the dots are much smaller and numerous. They
are slow and per page cost of running a laser printer because the cost of ink cartridge is high.
Advantage of inkjet printers:
a. It has high quality output.
b. It is good for printing pictures.
c. It is quieter than dot matrix.
d. No warm-up time.
Disadvantage of inkjet printers:
a. Its print head is less durable.
b. It is expensive since its replacement cartridge is expensive.
c. It is not good for volume printing (print lot of pages).
d. It is not fast as laser printer.
II. Laser printer:
They are more expensive than inkjet printers; their print quality is higher and faster. A separate CPU and memory are built
into the printer to interpret the data that it receives from the computer and to control the laser. It uses the principle of dot matrix
printers in creating dot like images. These images are created on drum, treated with magnetically charged ink powder known as
toner and then transferred from drum to paper. They are quieter and faster than dot matrix printer. Print resolutions ranges from
300-2400 dpi (Dot per inch).
III. Thermal printer:
They are used for presentations of graphics and high quality images. They are expensive and require expensive paper. It
uses color waxes and heat to produce images by burning dots on to special heat sensitive paper. Characters are printed by applying
heat to selected rods in print head. When heated rods press the ribbon against the paper, the wax melts and ink is transferred to the
paper, the characters are formed.
PLOTTER:
It is special kind of output device. It is like printer because it produces images on paper but the plotter is typically used to
print large format images, such as engineering drawings. They use ink pen or ink jet to draw graphic. Either single color or
multicolor pens can be employed. They are slow device.
The graphics and drawings produce by pen plotter are uniform, precise and are of good quality. They are expensive than