CRT Monitors - A CRT monitor is a desktop monitor that contains a cathoderay tube. A cathoderay tube (CRT) is a large, sealed glass tube. That front of the tube is the screen. Tiny dots of phospor material coat the screen on a CRT. Inside the CRT, an electron beam moves back and froth across the back of the screen to glow, which produces an image on the screen.

CRT monitors have a much larger footprint than do LCD monitors : that it, they take up more desk space and thus are not used much today. A CRT monitor's viewable size is the diagonal measurement of the actual viewing area provided by the screen in the CRT monitor. A 21 inch monitor, for example : may have a viewble size of 20 inches.