Several processing units:

☛ Contains a special purpose processor, called video controller or display controller

☛ Video controller: A fixed area of the system memory is reserved for the frame buffer, and the video controller is given access to the framebuffer memory.

Tow registers are used to store the coordinates of the screen pixels.

The value is stored in the frame buffer for this pixel position is then retrieved and used to set the intensity of the CRT beam Initially the x register is set to 0 and the y register is set to ymax.

Then the x register is incremented by 1, and the process repeated for the next pixel on the top scan line.