Screen or Monitor
CRT Monitors
A monitor is an electronic device used to display the output of a computer. The early monitors looked very much like old television sets and worked in a similar way. These monitors were called Cathode Ray Tube (CRT) monitors as they operated a stream of electrons in a vacuum tube. The inner surface of the monitor screen was covered with a photo luminescent material that glowed when struck by electrons. The luminescent material was arranged in horizontal rows of dots called pixels and the more rows of pixels there were, the greater the clarity or resolution of the image that could be produced. If one of the pixels could be expanded so that we could look at it, you would see that each pixel was made of three coloured dots in the primary colours of light, namely, Red, Green and Blue (RGB). This meant that if the pixel was to glow a purple colour then the electron beam would excite the green and blue dots in the correct proportion so that overall a purple pixel dot would appear on the front of the screen. The older monitors would scan every second row and when complete would return and scan the alternate rows instead. This is known as interlaced scanning.
LCD Monitors
The LCD (Liquid Crystal Display) monitor uses the properties of liquid crystals working with electricity to line the crystals up in the pattern of the image required. These monitors use far less electricity than CRTs and can also be made with a flat screen with a much lower mass. Other advantages include, very little flicker in the image, no burn in possibilities and the screen can be made in any size or shape. A disadvantage, however, is that there are limited viewing angles.
Touch Screen
A most useful device that acts as both an Input and an Output device is a Touch Screen. This allows you to directly input data using fingers or a stylus and the screen acts as an output device displaying your required information.