Each of the ghosts is programmed with an individual “personality”, a different algorithm it uses to determine its method of moving through the maze. Understanding how each ghost behaves is extremely important to be able to effectively avoid them. However, before discussing their individual behaviors, let’s first examine the logic that they share.

I’ve read some of the source material on this before—the way the ghosts are programmed in Pac-Man is an awesome tale of making the best of limited resources and of sharp and inspired design.

(via GameInternals – Understanding Pac-Man Ghost Behavior.)