External devices of PC computers are called peripheral devices because they are located at the periphery i.e. outside of the computer’s processor. They enable users to receive processing results performed by the computer, while other computers use these results for additional work. Inserting of the large amount of data in the computer will not be very useful unless we have opportunity to find out results of its processing by some external device. Most common external devices are monitor and printer. Monitors and graphic cards display text, graphics and images, while LCD-panels are more and more used for public presentations. Quality graphic cards can also display video clips on monitors. We can use printersto print text and graphics, from ready-made pictures to professional engineering blueprints. Some peripheral devices such as fax/modem can be either internal or external devices because theycan both receive and send data. Speakers are becoming standard part of multimedia computers which can reproduce music, human voice or speech synthesis.


Monitor or screen is an electric external device for displaying images sent from another device, usually from graphic card in the computer. On monitor we can track results of data processing and current activities. Its purpose is to display letters or images which can be moving or steady. The image usually displayed on monitor is created in graphic card, specialstructurewith the function of creating and recovering images. There are several different technologies used for monitors. Based on applied technology we shall present the following types of monitors:
1. Cathode Ray Tube Monitors(CRT)
2. Liquid Crystal Display Monitors(LCD)
3. Plasm monitors(ionized gas)

CRT monitors
This type of monitor possesses so-called cathode or vacuum tube. On one side of this tube there is a screen that is coated with phosphorus and on the other side is the neckwith electronics. Electronics emitthe rays of electrons which collide with phosphorus, creating the light of specific color, and the collection of those lights represents the image. Basic characteristics are frequency and space between pixels, i.e. spots which are expressed in millimetres. This was the most common type of monitor in the world before LCD and Plasm monitors appeared.

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