Modern slot machines have been mythologized by hundreds of Websites that purport explain how they work. "Every machine has a Random Number Generator", you are told. The RNG chip — as it's called — is constantly producing new random numbers that are used to determine how "spins" are resolved, or discarded.
While this may be true what all these slot machine experts don't know or won't tell you is that there is no such thing as a truly random number generator. Mathematicians have been chasing true random number generation for centuries. So far all we have devised are algorithms that cycle through large sets of "scattered" numbers.
These large sets are computed from what is called a "seed" value. The seed value might be hard-coded into the algorithm or it can be taken from the only on-board device that is constantly producing unique information: the computer clock used by all electronic machines. A computer clock, once calibrated, simply counts away from 0. It moves in only 1 direction until it is stopped (say, by a power shortage) or reset.
We install batteries in computers whose clocks are important enough to warrant continual reliability even during long power outages. A typical computer clock today might last for 2 years or longer on its battery power alone.
Even so, computer clocks may be recalibrated from time to time because they can run too fast or too slow. A computer clock is driven by the speed of the central processing unit. This speed is measured as the number of times electrical pulses are pushed through the circuitry every second.
Once in a while you may sit down at a slot machine whose clock has just been recalibrated to an earlier time; in that case, the slot machine will play forward through a sequence of "random" numbers that it has already generated previously.
In addition to the computer clock, the slot machine has several levels of difficulty. These levels of difficulty work as multipliers that are used to adjust how often the slot items line up. In other words, the statistical probability that 5 lemons will appear on your screen can be adjusted up or down with the flip of a switch (or a bit of electronic information).
If you have ever watched or participated in a slot machine competition, you'll notice that all the players receive far more wins than they normally would if they were just playing random machines on the floor. That is because all the machines used in the competition have been temporarily adjusted to pay off more often.
Mathematicians know that "random number generators" can only cycle through a finite sequence of numbers. We do our best to devise algorithms that produce very, very long chains of generated numbers. But the power laws of statistical averages work against us. Some seed numbers produce more statistical clusters of values that will be translated into payoffs than other seed numbers.
And regardless of how likely your string of randomly generated numbers is to pay you a great win, the statistical laws of probabilities also dictate that there will be statistical clusters of numbers more likely (or less likely) to pay off. All you can do is play through these strange sequences of "good" and "bad" luck.
A mathematician's job is to figure out how to make these predictable patterns seem more random. Restarting the algorithm with a new seed every now and then is one way to do that. In other words, the machine doesn't have to just play through the whole sequence of numbers that could be generated by its current seed. It can abandon that set of numbers at any point in time and start over, generating a new set.
These generated number sets reside in memory on the slot machine. The machine grabs a number from the table, uses it, and then goes back for another. If the slot machine's memory can handle a large enough table it may cycle through the table 2 or more times before generating a new one.
If you are playing a slot machine and it suddenly hesitates or pauses, it may be regenerating its table of random numbers. The modifiers used to govern how "lucky" the machine tends to be remain the same until a technician resets them; only the random numbers may change. But that is often enough for your luck to change, either for the better or the worse.
No mathematician can help you predict when a slot machine will pay off or when it's likely in a "dry spell", but if you are convinced that they seem to go through cycles — well, you're almost right. That's why we keep changing the data, so that it's not TOO cyclic and predictable.
Some casinos may scatter a few "lucky" machines across the floor, programmed to be a little more likely to pay off than the rest. Although there is no mathematical way to predict where these machines will be, it's almost certain they will be visible to as many casino guests as possible.