Computer Science Studies (BIT)

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Join date : 2012-11-09

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PostSubject: Output Devices    Output Devices  EmptySun Sep 08, 2013 5:33 pm

1.     Monitors:

A monitor (or screen) is the most commonly used output device. They come in many different shapes, sizes and forms. Size of the screen actually indicates the length of the diagonal, so a 17 inch screen has a 17 inch diagonal. The picture on a monitor is made up of thousands of tiny coloured dots called pixels. The quality and detail of the picture depends on the number of pixels that the monitor can display. The higher the number of pixels, the better quality the output.

The two types of monitor that you need to know about are Cathode Ray Tube monitors (CRT) and Thin Film Transistor monitors (TFTs)

Cathode Ray Tube monitors (CRT)

CRT monitor are large and bulky and have a glass screen which makes them fairly robust and difficult to damage. They produce quite a lot of heat so when you have an office with lots of them it could get quite warm. They are also fairly noisy compared to newer TFT monitors.

Thin Film Transistor monitors (TFTs)

TFT monitors used to be very expensive but now the price has come down they are beginning to replace all of the old CRT monitors. Not only do they look much nicer they take up a lot less space. They are quieter than CRT monitors and also create less heat.

They are easier to damage than CRT screens. A few sharp pokes at the screen with a pencil can cause lasting damage. Another disadvantage is that unless you have a very high quality TFT monitor, the colours and contrast are not so good as a CRT monitor and so the picture can look a bit dull.

2.     Printers:

Printers are another common output device. They are used to create a 'hard' copy of your work i.e. something that you can hold, hand to someone else or file away.

Laser printers:

Laser printers are used in many workplaces because they are quiet, they print a large number of sheets very quickly and they produce high quality documents.

They print in the same way as photocopiers. Powdered ink, called 'Toner', is fused onto paper by heat and pressure.


   High quality printouts - better than ink-jet or dot-matrix
   Fast printouts - faster than ink-jet or dot-matrix
   Prints very quietly - quieter than ink-jet or dot-matrix
   Cost per page is low - cheaper than ink-jet or dot-matrix


   Most expensive printer type to buy, especially colour lasers
   Toner is more expensive than ink-jet cartridges
   Expensive to repair - lots of complex equipment inside
   Fairly bulky - larger than ink-jet printers

Inkjet printers:
They are relatively cheap to buy and most of them can combine both black and white and colour printing at the same time.

These printers use cartridges which contain ink. They operate by heating the ink as it flows through the nozzle. The heating process causes a small droplet of ink to form. This is then released as a single dot which forms part of a letter or image. This is why the printouts often come out of an ink-jet printer still slightly wet.

Colour ink-jet printers are ideal for use at home where only a few documents need to be printed and the quality of the printout doesn't need to be perfect.

   Cheap to buy - cheaper than a laser printer
   More compact than a laser printer
   Cartridges cost less to replace than toners
   Produce good quality printouts better than a dot-matrix but not as good as a laser
   Speed - faster than a dot-matrix but not as fast as a laser


   Noisier than a laser printer (but not as noisy as a dot-matrix)
   Colour printing can be extremely slow
   Cost of printouts per page are more expensive than a laser printer
   Cartridges need to be replaced more often than a laser printer
   Ink will smudge while it is still wet
   Colours can become saturated and often don't look the same as on the screen
   If not used for a while, the cartridges can dry out

Dot matrix printers:

These were the first type of printers to be used in homes and schools but they are not used much nowadays.

They are also called 'impact printers'. The print head contains a grid of pins and different combinations of pins are pushed out to form different characters. The print head then hits a carbon ribbon leaving an imprint on the paper. This makes them fairly noisy as you can hear the pins striking the paper.

They are also useful when continuous paper needs to be used for example printing large quantities of invoices or bills. They can be printed onto paper with perforations and then separated by tearing once the printing is complete.

   Relatively cheap to buy
   Low operating costs
   Can print on continuous stationary
   Create carbon copies using carbonated paper


   Print quality is poor and important documents are not suitable to give to managers or customers
   Very slow - slowest out of all three printers
   Noisy - you wouldn't want one of these printing all day in the office
   Cannot produce colour copies

3.     Plotter:

Plotters are a specialist type of printer which is able to draw high quality images on very large pieces of paper, for example 3 foot wide by 10 foot long.

They are used by engineers, architects and map-makers to draw plans of buildings, diagrams of machines or large scale maps.

A plotter differs from a printer in that it draws images using a pen that can be lowered, raised and moved across the paper to form continuous lines. The electronically controlled pen is moved around the paper by computer controlled motors.
There are three different types of plotter:
Flatbed plotters - These hold the paper still while the pens move
Drum plotters - These roll the paper over a cylinder.
Pinch-roller plotters - These are a mixture of the two types above

·         Drawings are of the same quality as if an expert drew them

·         Larger sizes of paper can be used than most printers can manage

   Plotters are slower than printers because each line is drawn separately
   They are often more expensive than printers
   They do not produce very high quality text printouts

4.     Speakers:

Most computers are fitted with a small internal speaker which can produce beeping sounds to alert you if you make an error. Computers can also be fitted with a sound card (or chip) which will enable sound to be output through external speakers. These usually produce a much higher quality sound than the internal speaker.

   Everyone in the room can hear the output from the computer.
   They can help create an atmosphere or ambiance to accompany a presentation
   They help blind people to use the computer because text can be converted into sound


   The output from speakers can disturb others who are trying to work
   High quality external speakers can be expensive
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