In their hearts, computers are sequential beasts. Their power comes from being able to break down the largest tasks into tiny steps that can be performed one after another. Often, though, our users need to see things occur in a single instantaneous step or see multiple tasks performed simultaneously.
A typical example, and one that every game engine must address, is rendering. When the game draws the world the users see, it does so one piece at a time — the mountains in the distance, the rolling hills, the trees, each in its turn. If the user watched the view draw incrementally like that, the illusion of a coherent world would be shattered. The scene must update smoothly and quickly, displaying a series of complete frames, each appearing instantly.
Double buffering solves this problem, but to understand how, we first need to review how a computer displays graphics.