Slot machines are pretty simple. A random number generator (RNG) picks three random numbers, each of which corresponds to a stop on each reel, then machine spins the reels so that they stop on the spots selected by the RNG. The principle is the same for five-line video slots: five random numbers, one for each wheel.
Note that by the time the reels are spinning, the game is already over. The RNG has already selected the reels, and the reels spin sort of as a courtesy to the player. Slot machines don’t even need reels — you could just put your money in and the machine could tell you whether you won or lost. The presence of the reels makes no difference in the game.
The reels are weighted so that some symbols are more likely to hit than others. For example, the slot may pick a random number from 1-127, which selects the symbols as follows:
Blank (positions between reels)
This is not the actual chart for any slot I know of, just an example of the concept. If there are 22 stops on the wheel (11 symbols and 11 blanks between the symbols), you don’t have a 1 in 22 chance of hitting the jackpot symbol on a given reel. It’s more like 1 in 64. Obviously, this is really deceptive. If they were honest, casinos would have a disclaimer on each machine saying “Odds of hitting any symbol are not proportional to the number of symbols on the reel,” or something like that.
By the way, each reel is typically weighted differently. That’s why you’re more likely to get jackpot symbols on the first and second reels (building the suspense) while failing to hit the symbol on the third reel.
The RNG is always working, even when you’re not playing, picking 168bet thousands of 3-number combinations per second. The moment you press the button or pull the lever, the RNG picks its 3 numbers. So if you someone hits a jackpot on a machine you were just playing, relax, you wouldn’t have gotten it had you kept playing.
The odds of hitting the jackpot on a typical slot are about 262,144 to 1. The odds are the same on every spin. It doesn’t matter if the machine has been played for months or years without hitting the jackpot, the odds of hitting the jackpot on the next spin are ALWAYS the same. No slot is ever “due” to hit a jackpot.
If you don’t believe me, try this experiment: Flip a coin until you’ve flipped three Heads in a row. At this point Tails should be “due”, right? It’s not. Flip again and write down the result. Repeat the whole process, flipping until you’ve had three Heads in a row, then flipping again and recording the result. Do this until you have 50-100 results. You’ll see that you’re no more likely to get Tails after three Heads than you are to get a fourth Head. Likewise, a machine that’s been played for a year without hitting a jackpot is no more likely to hit the jackpot soon than one that’s been played for a week without hitting it.