FTA: "Today, the world has changed. Displays are made of pixels but they all have, or can cheaply add, a “frame buffer” — memory containing the current image. R

FTA: "Today, the world has changed. Displays are made of pixels but they all have, or can cheaply add, a “frame buffer” — memory containing the current image. Refresh of pixels that are not changing need not be done on any particular schedule. We usually want to be able to change only some pixels very quickly. Even in video we only rarely change all the pixels at once." The trouble is, the system has to be designed to accommodate the worst case. "Usually" and "rarely" are of no more use in video than they are in realtime 3D graphics.