Slot players win or lose according to the symbols that appear at the end of each spin. Various possible combinations of these symbols are ranked in order from most valuable to least valuable in the pay table. No one knows exactly how likely (or unlikely) a particular set of symbols is to turn up. That depends solely on how the slot machine’s computer is programmed. And the casinos keep that a secret. It is not the casinos themselves that create the slots – they buy them from slot manufacturers – but the casinos can specify the payback percentage they would like.
What exactly is the slot machine’s computer and how does it work?
The computer in the slot machine which determines how symbols appear is known as a Random Number Generator. This computer chip blindly selects a symbol from each reel in the machine and combines them for the chosen combination. The RNG is selecting symbols forever – even when it is inactive. When someone clicks on “spin,” the slot machine takes whatever combination was in effect at the time and makes the reels stop at those symbols. (So in reality, the slot already knows where to stop before the spinning ends.)
Now the odds of a symbol being chosen are never equal. If they were, there would be no house edge to speak of and the casinos would have no reason to provide slots. By making certain combinations less likely to appear than others, the casino gains an edge over players.
To help illustrate this, let us pretend that the Random Number Generator is a blindfolded archer and the slot symbols are scattered all over a wide area. Some symbols are more numerous than others. The most valuable symbols are the fewest; the least-paying symbols are the most common. Now the archer is shooting arrows in the air which can land anywhere in the field. What symbols do you think the archer will hit more often?
If you think it is the least valuable symbols, you are right. Because they are more numerous, the laws of probability make it more likely they will appear in the slot machine. That is how slots and the Random Number Generator work, and why the casinos always win.
A further point you should understand is that no one can read the “mind” of a Random Number Generator. It doesn’t really have one. Just like an archer who mindlessly launches arrows in the air not caring where they hit, so the RNG functions in a perfectly random manner.
It follows that no slot system can ever predict slot machines that use RNG technology. It also means that jackpots happen all the time, if invisibly. The times when we say someone won the jackpot are when a lucky player chanced upon the jackpot combination as the RNG selected it.
So to sum up, a slot machine uses a computer chip to control its reels. The odds of which symbols get chosen are always tilted in the casino’s favor. This process is all computerized and no human intervention on the part of the player can influence it.