Vector Scan or Random Scan Display in this technique, the electron beam is directed only to the part of the screen where the picture is to be drawn rather than scanning from left to right and top to bottom as in raster scan. It is also called stroke-writing display, or calligraphic display.

As shown in Fig., vector scan CRT display directly traces out only the desired lines on CRT i.e. If we want a line connecting Point A with Point B on the vector graphics display, we simply drive the beam deflection circuitry, which will cause beam to go directly from Point A to B. If we want to move the beam from point A to Point B without showing a line between points, we can blank the beam as we move it. To move the beam across the CRT, the information about both, magnitude and direction is required. This information is generated with the help of vector graphics generator.

In vector displays beam is deflected from end point to end Point, hence this technique is also called random scan. In this the picture can be draw in terms of line, one at a time. The refresh rate depends on the number of lines to be displayed.

Raster Scan Display in this technique the electron beam is swept across the screen one row at a time from top to bottom. As it moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. This scanning process is called refreshing. Each complete scanning of a screen is normally called a frame.

Raster scan is the most common method of displaying images on the CRT screen. In this method, the horizontal and vertical deflection signals are generated to move the beam all over the screen in a pattern shown in the Fig. Here, the beam is swept back and forth from the left to the right across the screen. when the beam is moved from the left to the right, it is ON. The beam is OFF, when it is moved from the right to the left as shown by dotted line in Fig. The refreshing rate, called the frame rate, is normally 60 to 80 frames per second.

Picture definitions is stored in a memory area called the frame buffer. This frame buffer stores the intensity values for all the screen points. Each screen point is called a pixel (picture element).

On black and white systems, the frame buffer storing the values of the pixels is called a bitmap. Each entry in the bitmap is a 1-bit data which determine the ON (1) and OFF (0) of the intensity of the pixel. On color systems, the frame buffer storing the values of the pixels is called a pixmap. Each entry in the pixmap occupies a number of bits to represent the color of the pixel.