A cathode ray tube (CRT) display is the technique used in most computer |monitors|. It relies upon selective irradiation of a phosphor-coated display screen to cause it to glow where dots (or |pixels|) are desired. Electron guns, fire a "beam" of electrons toward the screen which passes through a set of electromagnets, called a yoke. This deflects the stream to hit the appropriate area on the inside of the display screen. A filtering mask, a hole aligned to each pixel, prevents unintentional lighting of neighboring pixels. The beam sweeps across the screen and from the top to the bottom. This process is repeated dozens of times per second.
In ~monochrome displays~, one electron gun activates a single type of phosphor. In a |multi-color CRT display|, three different types of phosphor are used, each of which is doped with a different rare-earth element to cause it to glow a different color, either red, blue, or green. Color displays require three electron guns - one for each color. The horizontal and vertical passes are synchronized by the CRT controller which is part of the |video adapter|. This controls the type of image displayed.
