Part of the PDP-1’s novelty and usefulness came from an optional display system that allowed for manipulation, via a light pen, of objects displayed on the screen. The display was an ‘x-y’ display, meaning that it worked by having the user ‘paint’ a single point on the screen by specifying the x and y-coordinates of the point. As Ivan Sutherland had shown in his Sketchpad program, from the simple ability to plot a point one quickly ascended up the ladder of geometrical abstraction to lines (2-D) and then to planes (3-D).
The Type 30 display, as it is known, was designed by Ben Gurley, the PDP-1 system architect and logic designer. It was a complex design but one that offered unheard-of resolution, was highly reliable, and which provided a key piece of the puzzle in making a computer truly interactive. The PDP-1 could be ordered with a high-precision (4K x 4K) or color display as well.