While the results in slots are random and determined by a random number generator (RNG) within the game, there are some fixed parameters that determine the chance of winning. For example, the number of symbols for each type is fixed. More matching symbols on the reels can result in more frequent wins.

Online casinos fulfill this requirement for online slots by using a random number generator (RNG). The random number generator is an algorithm generated by a computer that online casinos use to randomize the results of a spin.