The electrons are emitted by an electron gun. These electrons pass through focusing and deflection systems. The beam of electron strikes at specified points on the phosphor-coated screen. The light of phosphor fades after some time, so the electron beam is repeated quickly of redraw pictures on the screen on the same point. The phosphor on-screen us of different persistences. In this beam will move across the screen, one row at a time. The direction of movement is top to bottom it is used in television when the beam move from top to bottom beam will be on or off so the pattern of spots is created information on and off pixels is stored is refresh buffer. The raster scan system can store information of each pixel position so it is suitable for realistic display of objects. For a random scan, the beam is directed only o selected parts of the screen. The beam will refresh the area on which the picture is drawn. The image is drawn on-screen line by a line such types of displays are also called vector display.