1. Monitor
A Monitor (or "screen") is the most common form of output from a computer. It displays information in a similar way to that shown on a television screen.
On a typical computer the monitor may measure 17 inches (43 cm) across its display area. Larger monitors make working at a computer easier on the eyes. Of course the larger the screen, the higher its cost! Typical larger sizes are 19 inch, 20 inch and 21 inches.
Part of the quality of the output on a monitor depends on what resolution it is capable of displaying. Other factors include how much contrast it has, its viewing angle and how fast does it refresh the screen. For example a good computer game needs a fast screen refresh so you can see all the action.
The picture on a monitor is made up of thousands of tiny colored dots called pixels. The quality and detail of the picture on a monitor depends on the number of pixels that it can display. The more dense the pixels the greater the clarity of the screen image.
A PC monitor contains a matrix of dots of Red, Green and Blue known as RGB. these can be blended to display millions of colors.
This is one RGB pixel of light
R + B = M (magenta)
B + G = C (cyan)
G + R = Y (yellow)
R + G + B = W (white)
The two most common types of monitor are a cathode-ray tube (CRT) monitor and a liquid crystal display (LCD).
Liquid Crystal Display (or "TFT" Display)
This is smaller and lighter than the CRT (see below), which makes them ideal for use with portable laptops, PDAs and Palmtops. Even desktop computers are using them now that their price has become comparable to CRT monitors.
Liquid Crystal is the material used to create each pixel on the screen. The material has a special property - it can 'polarize' light depending on the electrical charge across it. Charge it one way and all the light passing through it is set to "vertical" polarity, charge it another way and the light polarity is set to "horizontal". This feature allows the pixels to be created. Each tiny cell of liquid crystal is a pixel.
TFT (or Thin Film Transistor) is the device within each pixel that sets the charge. And so sometimes they are called "Liquid Crystal Display" referring to the material they use or they are called "TFT displays" referring to the tiny transistors that make them work. LCDs use much less power than a normal monitor.
Cathode Ray Tube
The CRT works in the same way as a television - it contains an electron gun at the back of the glass tube. This fires electrons at groups of phosphor dots which coat the inside of the screen. When the electrons strike the phosphor dots they glow to give the colors.
Advantages of monitors
- Relatively cheap
- Reliable
- Can display text and graphics in a wide range of colours
- As each task is processed, the results can be displayed immediately on the screen
- Output can be scrolled backwards and forwards easily.
- Quiet
- Do not waste paper
- No permanent copy to keep - the results will disappear when the computer is switched off.
- Unsuitable for users with visual problems.
- Only a limited amount of information can be displayed at any one time
- Screens are made of glass and can be very fragile.
Printer
Printers are output devices. They are dedicated to creating paper copies from the computer.
Printers can produce text and images on paper. Paper can be either separate sheets such as A4 A5 A3 etc. or they may be able to print on continuous (fanfold) paper that feed through the machine.
Continuous paper with holes on the edges, used by dot matrix printers. After you print on fanfold paper, you have to separate the pages and tear off the edge strips
Very specialist printers can also print on plastic or even textiles such as T-shirts.
Some printers are dedicated to only producing black and white output. Their advantage is that they are often faster than a color printer because effectively there is only one color to print (Black).
Color Printers are dedicated to creating text and images in full color. Some types can even produce photographs when special paper is
used.
There are three main types of printer that you need to know about. You will be expected to understand the main differences i.e. purchase costs, running costs, quality and speed
The three types are Laser, Dot Matrix and Inkjet.
Plotter
These are output devices that can produce high quality line diagrams on paper. They are often used by engineering, architects and
scientific organizations to draw plans, diagrams of machines and printed circuit boards.
A plotter differs from a printer in that it draws images using a pen that can be lowered, raised and moved across the page to form
continuous lines. The electronically controlled pen is moved by two computercontrolled motors. The pen is lifted on and off the page by switching an electromagnet on and off.
The paper is handled in different ways depending on the type of plotter. Flatbed plotters hold the paper still while the pens move. Drum plotters roll the paper over a cylinder Pinch-roller plotters are a mixture of the two.
Advantages:
- Drawings are of the same quality as if an expert drew them
- Larger sizes of paper can be used than would be found on most printers
- Plotters are slower than printers, drawing each line separately.
- They are often more expensive to buy than printers
- Although drawings are completed to the highest quality they are not suitable for text (although text can be produced)
- There is a limit to the amount of detail these plotters can produce, although there are plotters which are "pen-less" the set are used for
- high-density drawings as may be used for printed circuit board layout.
- In recent years, cheaper printers that can handle A3 and A2 sized paper have resulted in a decline in the need for smaller plotters.
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