A. Hard copy output devices:- The output is printed by a computer on to a paper or some other material which can be used to show to others and the printed output can be filed which can be used at a later stage. These devices are printers and plotters.
B. Soft copy output:- This type of output can be seen on the screen of a monitor and cannot be stored for future use. These devices are monitors and voice response systems.
1.Visual display unit (VDU)
The visual display unit forms the basis of an interactive terminal. It contains a cathode-ray-tube (CRT) which is similar to the monitor used for television. This forms an output unit and is complemented by a keyboard used for input of characters. The VDU is backed by a RAM memory where all the displayed characters are held. A video display terminal act as either a remote terminal connected to a computer through external circuit or a local terminal within the same building. It may even be integrated to the CPU as a computer console. Being in a conversational mode with the computer it uses the VDU for acknowledging inputs, pointing output errors and displaying comments.
Operation:- The depression of the key on the keyboard, causes a binary code to be generated which identifies the key. The code may be immediately transmitted to the computer which stores and processes it and if relevant transmits it back to VDU memory for display. This is referred to as 'echo'. If in local mode ( not in line the computer) it may handle its own display and terminal memory and allow the user to compose a message.
Output features:- The screen attributes may be controlled by the user. Software controllable character attributes may be in the form of:-
A. Blinking fiels,
B.Reverse video-for foreground and background colours are interchanged
C. Colour setting,
D. Intensity setting.
TYPES OF MONITORS
A. Monochromic:- These VDU's use foreground or background colours chosen according to human eye sensitivity.
B. Colour:- Colours are formed by super position of controlled intensities of red, green and blue dots.
2. Printers:- A printer is an output device which gives output in printed form called as hard copy. Printers can be classified into following two categories:-
a. Impact printers:-These printers print the character by physically striking the typing devices against an inked ribbon and paper.
b. Non Impact printers:- These printers form the character by using heat, ink and laser beam. There is no physical contact between paper and ribbon.
IMPACT PRINTERS:-
Line printers:- The speed of such pronters is about 300 lines per minute. These printers are useful where the data volume is large. The drawback of these printers ia that they do not support graphics. These printers are of two types:-
A. Chain printers:- As the name indicates these character set of a chain printer revolves at a high speed representing each character in turn all along the length of print line. Print hammer hits at approprite point as the letter files past.
B. Drum printer:- It is also called as barrel printer. It has a drum around which there is a complete set of characters. These are in equal number of small hammers, one per character and inked ribbon lies between the character and character and printing. Each character in turn is presented by rotation of a drum and similar characters in a line are all printed simultaneously. One complete line is printed in one complete rotation of the drum.
CHARACTER PRINTERA:-
A. Dot matrix printer:- These printers do not have characters embossed or otherwise in view. The arrangement of tiny hammers or pins strike the ribbon to produce the desired characters. These tiny pairs in a matrix of 7 dots across 9 dot down. These printers are noisy but can print text and graphics.
B. Daisy wheel printers:- These printers use a daisy wherl is a flat disk having a set of spokes. Each spoke has a single character embossed at the top. The hub of the wheel rotates to bring the desired character into position and in turn is struck by a hammer mechanism to form the image on the paper
Daisy wheel printers are available in many types of fonts which can be interchanged in quality. These printers are mainly used in word processing applications. Where high quality printing is required. The speed of such printers lies between 25-60 characters per second.
NON IMPACT PRINTERS:-
A. Laser printers:- Laser printer produce very high quality printing with sharp images. Laser technology is used in such printers and a microprocessor controls the laser beam. The output quality of these printers is very good and these printers are fast jn speed. The cost of these printers is also high.
B. Inkjet printers:- These printers are very popular these days. The technology used in these printers is similar to dotmatrix printers but instead of using ribbon, ink is forced out of tiny holes directly on the paper to form characters. The inkjet printers are higher priced than dot matrix printers. The print quality of these printers is closer to that of laser printers. We can also have a colour print out from these printers.
3. Plotters/Tracers:- A plotter is a printer which is used to create presentation visuals, charts and diagrams prepared from statistical data. In a plotter a pen moves up and down on the paper and draws figures or writes text.
A plotter can be connected to a PC through parallel port. A plotter is a software dependent and needs much more instructions than a printer to produce an output.
4. Speech synthesis:- When some voice is recorded then the components of sound are broken into digital components i.e. '0' and '1' and are stored. Then these digital signals are converted into sound waves. A computer can be designed for few words and sojnds. Such microprocessor devices are very much familiar today which can produce different tones.
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