This question gets a lot simpler once you realize how they were originally implemented and many still are today: state machines. There is no history, no FIFO, t

This question gets a lot simpler once you realize how they were originally implemented and many still are today: state machines. There is no history, no FIFO, the only thing that exists is the now. It's lot easier to answer, "I'm going up and am on the 3rd floor, someone is waiting on the 4th floor, do I start slowing down?" Then it is to answer, "someone pushed up on 4th and someone pushed down on 7th.... etc.". This is also why many elevators perform very poorly under heavy load. You want to skip floors when the elevator is already full.