Output devices

An output unit of a computer system performs the following functions:

It accepts the results produced by the computer, which are in coded form and hence, cannot be easily understood by us
It converts these coded results to human acceptable (readable) form
It supplies the converted results to outside world

Commonly Used Output Devices

Monitors
Printers
Plotters
Screen image projector
Voice response systems

Types of Output

Soft-copy output

Not produced on a paper or some material that can be touched and carried for being shown to others
Temporary in nature and vanish after use
Examples are output displayed on a terminal screen or spoken out by a voice response system

Hard-copy output

Produced on a paper or some material that can be touched and carried for being shown to others
Permanent in nature and can be kept in paper files or can be looked at a later time when the person is not using the computer
Examples are output produced by printers or plotters on paper

Monitors

Monitors are the most popular output devices used for producing soft-copy output
Display the output on a television like screen
Monitor associated with a keyboard is called a video display terminal (VDT).
It is the most popular Output device

Types of Monitors

Cathode-ray-tube (CRT) monitors look like a television and are normally used with non-portable computer systems
Flat-panel monitors are thinner and lighter and are commonly used with portable computer systems like notebook computers. Now they are also used with non- portable desktop computer systems because they occupy less table space.

Printers

Most common output devices for producing hard-copy output

Dot-Matrix Printers

Character printers that form characters and all kinds of images as a pattern of dots
Print many special characters, different sizes of print and graphics such as charts and graphs
Impact printers can be used for generating multiple copies by using carbon paper or its equivalent
Slow, with speeds usually ranging between 30 to 600 characters per second
Cheap in both initial cost and cost of operation

Inkjet Printers

Character printers that form characters and all kinds of images by spraying small drops of ink on to the paper
Print head contains up to 64 tiny nozzles that can be selectively heated up in a few micro seconds by an integrated circuit register
To print a character, the printer selectively heats the appropriate set of nozzles as the print head moves horizontally
Can print many special characters, different sizes of print, and graphics such as charts and graphs
Non-impact printers. Hence, they cannot produce multiple copies of a document in a single printing
Can be both monochrome and color
Slower than dot-matrix printers with speeds usually ranging between 40 to 300 characters per second
More expensive than a dot-matrix printer

Laser Printers

Page printers that print one page at a time
Consist of a laser beam source, a multi-sided mirror, a photoconductive drum and toner (tiny particles of oppositely charged ink)
To print a page, the laser beam is focused on the electro statically charged drum by the spinning multi-sided mirror
Toner sticks to the drum in the places the laser beam has charged the drum’s surface.
Toner is then permanently fused on the paper with heat and pressure to generate the printer output
Laser printers produce very high quality output having resolutions in the range of 600 to 1200 dpi

Plotters

Plotters are an ideal output device for architects, engineers, city planners, and others who need to routinely generate high-precision, hard-copy graphic output of widely varying sizes

Two commonly used types of plotters are:

Drum plotter, in which the paper on which the design has to be made is placed over a drum that can rotate in both clockwise and anti-clockwise directions
Flatbed plotter, in which the paper on which the design has to be made is spread and fixed over a rectangular flatbed table

Screen Image Projector

An output device that can be directly plugged to a computer system for projecting information from a computer on to a large screen
Useful for making presentations to a group of people with direct use of a computer
Full-fledged multimedia presentation with audio, video, image, and animation can be prepared and made using this facility

Voice Response Systems

Voice response system enables a computer to talk to a user
Has an audio-response device that produces audio output
Such systems are of two types:
Voice reproduction systems
Speech synthesizers