Taking back moves

One thing I wish the chess program did is load moves I've already done. For example, let's say I take back a move or two :) It would be nice for the computer to store that incase I want to go back to that. Perhaps take that into account with the ai. (Hey it would be fair for the computer since it would let me take back a move). Anyway, I like playing chess on hard. Gives my brain a workout.