An introduction to computer graphic terminals

The purpose of this paper is to introduce the reader to some of the fundamental hardware and software aspects of typical CRT display consoles. Techniques for accomplishing display refresh are explained. The evolution of the CRT controller, from a device which simply includes a pair of digital-to-analog converters to a system which is a rather sophisticated, special-purpose hybrid processor (including analog function generators and digital control logic), is developed. Means by which a user generates display processor interrupts, particularly those associated with graphic input devices, are described. The use of electronic "pens" for user interaction with a display is then explained. Finally, the software structure for a typical graphic processor is discussed from a functional point of view. The linkage between a high-level symbolic picture description and the CRT "machine language" display file, via a set of generation subroutines, is described. The calling of picture modification programs by an interrupt analysis routine is also explained. Reasons for the need of a linked-list data structure are presented.