For displaying large quantities of alphanumeric data,the readout system employed most commonly  is a familiar CRT.CRTs form the basis of CROs and TV systems.To generate characters on the CRT,the generation system of characters on CRTs requires relatively simple electronic circuitry.

A typical CRT display has easy facilities for the control of digit size by controlling the deflections sensitivity of the system.The number of characters displayed can be changed with the help of time shared deflection and modulator circuits.

On a CRT display the intensity and brightness can be realized,with different gray scales,and the display can have different colour depending on the phosphor used in the screen.Generally the phosphor is chosen to be white or green.

Storage type CRTs facilities storing a stationary pattern on the screen without flickering display and it is possible to retain the pattern for a long time independent of the phospher persistence.