6. Output Devices

These are devices used to 'see' the results of any processing of any data entered into the computer through any of the input devices described earlier.

 

1. Printers

Computers were supposed to bring about the dream of a 'paperless office'. This now looks very unlikely to happen because paper has got some advantages over computers when looking at information.

Advantages of Paper

1. It is very portable. The information on a sheet of paper is easily passed around, and many people can look at the information at the same time.
2. It is cheap. Initial costs of computers means there is no comparison with the cost of using paper.
3. Not everyone has computer equipment to view information, or it may
   be difficult to use computers in some situations.

Paper copies, or hard copies, of information will always be needed. Printers (and plotters) are used to produce these hard copies. The main different types of printer, and how they are compared against each other, are explained below.

 

 

a. Laser Printers

This type of printer is the main one used in schools, offices and industry because it produces high-quality printouts very quickly, with good resolution.

How it works?

• It uses a laser to make a negative electrical image of the page on a positively charged drum, which then picks up positively charged toner.
• The drum rolls over the paper and the toner is heated to print on to the page. The toner cartridge gives many copies before needing replaced keeping running costs down.
• Laser printers are generally more expensive than inkjet printers, but their running costs are lower.

 

b. Inkjet Printers

:Basic models of this type of printer are cheap to buy, and let you print in colour.
The quality of the best inkjet's can be very high and can be used for photographs.

• Inkjet printers spray special ink on the paper to form characters and graphics.
• The cost of replacing ink cartridges can be high with this type of printer because they need replaced frequently.
• They print quite quickly, but can be quite slow when printing graphics.
• They are slower than laser printers.

 

Movie: 11. Printers

 

 

2. Plotters

Plotters are large printer type devices. Instead of using ink cartridges, plotters use pens to draw the output on to paper. With different coloured pens, plotters can produce colour output.

Plotters are capable of producing very accurate drawings and plans. They are most often used in computer aided design (CAD).

 

 

 

The picture partly shows some 'blue prints' produced by a plotter.

 

 

 

 

 

3. Sound Card and Speakers

A sound card captures sounds and changes them into digital binary numbers that are stored as files in your computer.

When outputting sounds the sound card reverses the process and changes binary data held in the sound files into analogue signals that are used control the speakers attached to the computer. Speakers convert analogue audio signals into the equivalent air vibrations in order to make audible sound. A pair of speakers plugs into the computer’s sound card.

 

A good sound card is necessary to get the best gaming experience.

 

Movie: 12. Sound Card

 

 

 

 

 

4. Screens and Monitors

Screens are the most common of output devices. They show what's going in the computer. There are really three main types.

1. Liquid Crystal Display (LCD) Screens.
2. Thin Film Transistor (TFT) Screens.
3. Cathode Ray Tube (CRT) Screens

 

 

 

 

 

Choosing and Comparing Printers

When we compare printers we should look at the following characteristics.

Set-up costs

This is a little tricky because it seems at first that inkjet printers are really cheap. The initial cost or capital cost can be very low with a new inkjet printer costing as little as £60. This is not the whole story because inkjet's can have expensive running costs.

Running costs

After you buy a printer these other costs become important.

1. ‘Consumables’ (ink refills, toner for laser printers, special paper) need to be bought regularly and the cost of these vary from printer to printer.
2. Colour inkjet cartridges can be very expensive at around £20 each. Depending on how much printing you do you can soon end up paying more for the ink than the printer itself!

 

Resolution (Print Quality)

Resolution is measured in dots per inch (shortened to dpi). This is used to measure the quality of the printout. Let us take the example of a resolution of 300 dots per inch. That means that for each square inch there are 300 x 300 dots = 90,000 dots. The higher the number of dots per inch the sharper and clearer the image will be.

 

Speed

We should look at how long they take to print a page. Different printers have different printing speeds. Measured in ‘pages per minute’ (ppm), faster printers are normally more expensive and are often networked to allow many users to take advantage of the speed.

The cost of repairs may also need to be considered for expensive printers.

Summary Table

 

Printer	Set-up Cost	Running Cost	Speed	Resolution
Laser	High	Low	Fast	High
Colour Laser	Very High	High	Fast	High
Inkjet	Low	High	Quite Fast	Very High

 

 

 

What you have to do!

Watch the videos above and in your Word document or your Brain complete the following exercises.

1. What are the characteristics or criteria you would use to choose a printer.
2. What is hard copy?
3. Briefly explain how sound cards and speakers are used to produce sound.

 

 

What you should be able to do!

1. Explain the role or purpose of output devices.

2. Provide examples of a number of output devices.

3. Choose or recommend a printer for given situations.

 

Continue to 7. Screens and Displays