Output devices
Introduction
In this section, we will discuss suitable output devices for a wide range of situations. Before we begin, however, it is worth taking note of the common computing term 'peripheral'. A peripheral device is an input, output or storage device that you connect to your CPU. You usually do this by plugging a device in to your computer, often into a USB port. The port then makes the necessary connections inside the computer to the CPU. All output devices are also peripherals.
Dot matrix printers
These are relatively slow and noisy and the quality of the hard copy is relatively poor compared to ink-jets and laser printers. They were very common a few years back in the early days of computing. Their uses are far more limited now but they do have one particular advantage. The hard copy is made by pins striking paper. That means that identical copies can be made of a printout by using carbon paper between sheets of paper. This system is used by credit card companies to produce actual copies of receipts when a customer makes a purchase. After a customer's credit card is swiped and authorised, two identical copies of a receipt are printed using small dot matrix printers. Both copies are then passed to the customer, who signs the top copy. This puts a carbon signature on the bottom copy. The customer keeps one copy and the shop keeps the other. You cannot make actual carbon copies with ink-jets or laser printers although of course you can print out two copies of a document!
Ink-jet printers
This type of printer 'sprays' ink onto paper.
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- An ink-jet printer can't produce carbon copies.
- An ink-jet printer can produce very high quality black and white as well as colour copies for a very low cost.
- It's a good choice for low volume situations e.g.homes.
Laser printers
These types of printers are in widespread use.
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- A laser printer produces very high quality black and white hardcopy.
- A laser printer costs more to buy and run than ink-jets although costs have been steadily falling in recent years.
- The price of colour laser printers has been falling to make them within reach of individuals and small businesses.
- Refills are expensive compared to ink-jets.
Plotters
Plotters are widely used in some industries.
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- Plotters are used to plot very large drawings such as those needed by engineers and designers whereas standard printers commonly only print up to A4 (and sometimes A3).
- Plotters produce very high quality, very accurate, colour drawings.
- Plotters are relatively expensive compared to printers.
Visual Display Units (VDU)
Monitors or computer screens are ideal for displaying data and information to users. They come in a range of sizes. Larger ones such as 21-inch screens, for example, would be ideal for engineers using Computer Aided Design software applications. 15-inch screens are perfectly acceptable for users using a range of generic applications. CRT (Cathode Ray Tube) monitors (similar to televisions) do take up a lot of space on a desk. Flat panel liquid crystal display screens, often referred to as TFT screens, save a lot of space by comparison. They are not quite as sharp as CRT screens, however, and are more expensive. TFT screens produce less radiation than CRT monitors. Excessive exposure to radiation is seen as a potential risk to computer users. They also use about half the power a CRT screen uses. If you multiply up the savings in power use in an organisation with thousands of computers, the cost-savings do become significant.
Speakers
Some applications such as burglar alarms, factory warning systems and monitoring equipment make use of audio output. Some applications also require sound, such as video-conferencing, using your computer to make phone calls, listening to DVDs or CDs and playing games. There are different ways that audio output from a computer can be achieved.
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- The cheapest option is simply a pair of speakers powered by the computer. They will plug into the back of the computer, in the speaker output. The quality and level of sound will be perfectly adequate for many applications but they cannot produce a very loud output and cannot produce a very high quality sound.
- You could also buy a pair of speakers that come with their own power supply. Although more expensive, they produce a higher quality sound and greater volume.
- It is perfectly possible to connect an amplifier to the back of a computer and then pass the amplified signal to some speakers. This is a much more expensive proposition but does produce hi-fi quality sound.
- In some noisy environments such as factories, klaxons (sometimes known as 'sirens') are common. These can be computer controlled and can produce a very loud sound that can be heard over noisy machinery.
Headphones
There are situations where a user wants to listen to sound in a public place but doesn't want to disturb others. For example, a user in a library might want to listen to CDs on a computer, or a telesales operator might need to concentrate on what a customer is saying.