The cathode-ray tube (CRT) is vacuum tube used as a display screen in a computer or video display terminal. CRTs are the most common softcopy output devices used with computer systems; this technology is also used in TV sets.
The CRT’s screen display is made up of small picture elements (dots), called pixels for short. A pixel is the smallest unit one the screen that can be turned on or off or made different shades.
A stream of bits defining the image is sent from the computer to the CRT’s electron gun, wherever the bits are regenerated to electrons. The inside of the front of the screen is coated with phosphor. Once a beam of electrons from the electron gun (deflected through a yoke) hits the phosphor, it lights up chosen pixels to generate a picture on the screen.