OUTPUT DEVICES

Output device displays result of the computer processing for user. The popular output devices are monitor, printer and speaker (audio response systems).

1. Visual Display Unit or Monitor

Visual display units (VDUs) are television-like screens that provide the user-interface in the form of display of text, numbers and images. The VDUs may be monochrome or colour. The support of monochrome or colour and clarity of display depend on the type of video monitor and the video adapter installed in the microcomputer.

The video display terminal (VDT) consists of a monitor or CRT and a keyboard. The CRT serves as an output device and the keyboard as an input device. Thus VDT is an input/output device. If the terminal is provided with some memory and certain processing capability, it becomes a smart or intelligent terminal. A terminal without processing power is called a dumb terminal.

2. Speaker and Audio Response Systems

Computer can produce verbal output where the output or response can be standardized as replies to special requests for information. The unit analyses the input and delivers the verbal reply by assembling the responses from pre-recorded words and phrases.

3. Printers

Printers are purely output devices. They produce hard copy output. Computer printers vary widely in their technologies and capabilities. They can be classified in a number of ways. First, they can be classified into three broad groups: character printers, line printers and page printers.

They can also be classified into impact and non-impact printers based on the basis of the printing mechanism.

The impact printing technology uses some mechanical pressure to produce images on paper. The impact printers include dot matrix printer, daisy wheel printer and chain printer. It is possible to

take multiple copies of output with impact printers. Non-impact printers do not use mechanical force to produce output on paper and hence they can produce only single copy output. Thermal

printer, Inkjet printer and laser printer are all non-impact printers. Of these several types of printers, dot matrix printer, inkjet printer and laser printer are very poplar.

3.1 Dot Matrix Printer (DMP)

DMP prints one character at a time as a set of dots produced by the pins on the print head. It uses a nine or twenty-four pin print head. The pins or printing wires are aligned into the shape of the character to be printed before the print head strikes the ribbon. The impact of the strike produces character shapes on paper. The speed of DMP is measured in character per second (CPS). A normal dot matrix printer with nine or twenty-four pin print head can produce output ranging from 50 to 600 characters per second. It produces lot of noise when working. The popular DMPs are Epson, Panasonic, Citizen, Wipro, TVSE and Lexmark. The operating cost for DMP is the lowest among all types of printers.

3.2 Inkjet Printer

Inkjet is a non-impact printer and is quiet when working. It sprays ink particles through its nozzle. On leaving the nozzle, the tiny particles of ink get electrically charged. The electrically charged particles are then guided on to the paper to form appropriate characters. Inkjet printers are as cheap as dot matrix printers are; but their operating costs are far higher than those of dot matrix printers. However, they give much better quality than DMPs. They are available in black and white and colour. The popular brands of inkjet printers are Hewlett-Packard, Epson Stylus and Canon.

3.3 Laser Printer

Laser printer is a high-end printer. It is more expensive than inkjet printers and its operating costs are also higher than inkjet printers. It uses the same technology as that of Xerox copier machines and it can produce both character and graphic output. It gives the best quality output. Though expensive, laser printer is becoming increasingly popular.

3.4 Daisy Wheel Printer

The daisy wheel printer has a wheel with a number of spokes made up of metal and plastic. Each spoke carries a typeface at the outer end. The wheel rotates until the appropriate character

comes under the hammer, which strikes to produce the impression on paper. These wheels are inexpensive and removable. It is slow and produces noise like dot matrix printer; but it gives fine quality output.

3.5 Thermal Printer

The thermal printer generates heat to produce the required character shape on specially coated thermal paper. The print head, which carries electric current, burns the aluminium coating on the paper into the character form. It is a quiet printer.

3.6 Drum Printer

It is a line printer. It has a drum that rotates at high speed. A set of characters is embossed on the drum. It prints one line of characters at a time. The hammer for a particular character position is activated when that character on the drum passes under it to produce character impression on paper.

3.7 Chain Printer

'The chain printer works like the drum printer. It consists of a set of typefaces on a chain that rotates at high speed. The printer composes one line at a time and the hammers are activated to produce one row of characters as it is composed. There is a hammer for each print position. As the characters move around on the chain, the hammer strikes on the opposite side of the print position to produce character impression on paper.

3.8 Magnetic Printer

In a magnetic printer, a drum coated with magnetic material captures the image of the page to be printed. These magnetic spots attract dry ink particles, which are then pressurised and transferred to paper to produce output.

4. Graphic Plotters

Plotters are used for plotting graphs and designs on paper. Architects and designers use plotters to produce blueprints of their designs on paper. It is a specialised output device for preparing computer drawn charts and graphs. The most popular type of plotter is the flat bed device. It plots on paper (or other material) that is spread on a flat bed.