Raster Scan Systems

Interactive raster graphics systems typically employ several processing units. In addition to the central processing unit or CPU, a special purpose processor, called the video controller or display controller, is used to control the operations of the display device.
The frame buffer can be anywhere in the system memory, and the video controller accesses the frame buffer to refresh the screen. In addition to the video controller, more sophisticated raster systems employ other processors as co-processors and accelerators to implement various graphics operations