Casino slot machines generate random numbers continuously at very high speed and use the most recent result(s) when the user pulls the lever (or hits the button) to spin the reels.
Even a simplistic generator can be used. Even if you knew the algorithm used, you cannot observe where in the sequence it is because nearly all the results are discarded. If somehow you did know where it was in the sequence, you'd have to have millisecond or better timing to take advantage of it.
Modern "mechanical reel" machines use PRNGs and drive the reels with stepper motors to simulate the old style spin-and-brake.
- http://en.wikipedia.org/wiki/Slot_machine#Random_number_generators
- http://entertainment.howstuffworks.com/slot-machine3.htm
