OUTPUT DEVICES

‘Output’ means to produce the results of processed data. The most common types of output are:

1. Hardcopy – this is called permanent output since it is printed for review away from the computer, e.g. reports and pictures.

2. Softcopy – this is not permanent output.  It includes output from a computer monitor, audio (sound) from speakers, electrical signals from modems and output from one computer to another.

Definition:  An output device gets processed information out of a computer.

Output devices include the following: monitors (display devices), printers (impact and non-impact), plotters, speakers, microfilm etc.

MONITORS (DISPLAY DEVICES)

Computers display output on a screen or monitor.  A monitor contains a matrix or array of luminescent dots of red, green and blue (known as RGB).  These can be blended to display millions of colours.  Mapping the location and colour information of each bit of data creates an image or bitmap (bmp) on the screen. The bitmapped image on seen on a monitor is made up of thousands of pixels.

Pixel stands for picture (pix) element.

Types of monitors:

1. Cathode Ray Tube (CRT)

2. Liquid Crystal Display (LCD)

Features of a computer screen

1. Size – this is the dimension of the screen which shows the output.  Common desktop screens range from 14 inches to 19 inches.  The size of a monitor is obtained by measuring the screen diagonally.

2. Resolution – this determines how clear and detailed the output on the screen can be.  Pictures on a screen are made up of tiny dots

(1 dot = 1 pixel).  The more pixels per inch, the clearer and more detailed the graphic.

3. Colour – the number of colours displayed can vary from 16 to 16.7 million.  The more colours, the smoother the graphics appear, especially photos.

PRINTERS

Printers are devices which output a hardcopy of your work. 

Types of printers

1. Impact printers

2. Non-impact printers

Impact Printers

Impact printers strike through a carbon or inked ribbon, like a typewriter. They are noisy and do not usually print acceptable graphics.  However, they are useful for printing multiple copies of documents using carbon paper.

1. Dot-matrix Printer – this type of printer uses pins to print a pattern of dots on paper. 

Advantage: relatively low cost. 

Disadvantage: poor quality of printing, readable but cannot be copied or used for business letters

2. Line Printer – the characters in line printers are on a cylinder.  Each segment of the cylinder has a full set of characters in raised form around the edge.  One complete line of text is printed during one revolution of the cylinder.

Advantage: faster than other impact printers

Disadvantage: All the ‘A’s found in the text on that particular line are printed first, then all the ‘B’s and so on until all the letters that make up the words have been printed and the line is complete.

Non-Impact Printers

These printers do not involve actually striking the paper.  Instead, ink spray or toner is used and the characters are fixed onto the paper by heating.  Since the printing element is simple and has no moving parts, these printers are inexpensive to manufacture. They also print documents quickly and are silent.

1. Ink-jet Printer – these printers operate by spraying small droplets of ink onto the paper.  Speeds of 4 to 6 pages per minute may be achieved.  The quality of the printout can be nearly as good as that of a laser printer.  Most suitable for use at home.

Disadvantages:

     a. Slower than laser printers

     b. The print heads become filled with ink and must be cleaned

     c. Ink cartridges need to be replaced more frequently than toner cartridges of laser printers

2. Laser Printer – these printers produce attractive documents at a high resolution and are much faster than ink-jets.  They are used in many workplaces because they are quiet, print quickly and can be stocked with a large number of sheets of paper and produce very high-quality documents.

In the laser printer, the paper is charged electrostatically and attracts dry ink powder and the pattern is then baked unto the paper. Many lines are printed simultaneously and speeds of 8 to 12 pages per minute can be achieved.

Disadvantage: Colour laser printers are far more expensive than colour ink-jet printers.

PLOTTERS

A plotter uses colour pens or toner to draw an image on paper.  The paper is handled in different ways depending on the type of plotter.

a. Flatbed plotter – the paper remains fixed while the pens move.

b. Drum plotter – rolls the paper over a cylinder. This type of plotter can produce very large drawings.

Plotters are mostly used by Car Designers, Architects and Engineers to print accurate charts, diagrams and 3D drawings.

AUDIO OUTPUT DEVICES (SPEAKERS, HEADPHONES, EARPHONES)

Used for the delivery of audio (sound) output.

MICROFILM

These are used as an alternative to paper.  The output is ‘printed’ on a roll of film(computer output microfilm) or a sheet of film (computer output microfiche) rather than paper.

Advantage: faster and it condenses large stacks of paper into small amounts of microfilm or microfiche with no special programming.

Disadvantage: uses a special device to print the microfilm and a special viewer to read it.

OTHER TERMS TO NOTE

1. Human-readable – output that can be understood by humans, eg. printed documents and output on a screen.

2. Machine-readable – output is in a form that only a computer can process.