VDU Displays

These are the most common output device. The display can be monochrome or colour and it is capable of presenting text and graphics. Running costs are low and output is silent.

The display is composed of a number of closely spaced dots. Dots that are more closely packed, being smaller, produce a higher quality display. Typically a VDU would have 1024 x 768 dots or pixels - this is the Super VGA standard.

A normal VDU has a picture created by firing an electron beam at a screen. When the beam hits a point on the screen a phosphorescent dot glows for a short time. The beam scans the whole screen so quickly that the eye does not notice the continual glowing and dimming of the dots. The beam is controlled by electromagnets. A fairly large space is needed behind the screen to provide a sufficiently long path to create and control the electron beam. This means that it is unlikely that this type of VDU will get much smaller. The power requirements of a VDU are also fairly large compared to those of the processor. This, together with the size of the display, makes them unsuitable for portable or battery operated systems.

A Fuller account of how these work is in the section 2.

Liquid crystal displays are used for laptop computers. They have the advantages of low power consumption compared to cathode ray (electron beam) devices; they are lighter and have a flat profile. However they are more expensive to produce, particularly if a larger size screen is required and the display works more slowly than the traditional cathode ray screen. A fuller account of LCD is found in section 2

Some applications, such as CAD, require higher than normal resolution. In this situation a Graphics Workstation would be used.

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