Nowadays, the majority of slot machines are designed in this way so they can function to call to mind their old mechanical predecessors.
The old patriarchal machines have had 3 reels, with twenty symbols on every reel. Practically, it works out to 20 X 20 X 20 combinations that could ever exist, this means a 8000 to 1 chance to hit the big prize.
Today, all of them have some computer chips that are operating inside, and these 20 symbols are computerized stops. So, the possibility to hit the big jackpot is one in 256 X 256 X 256.
Even the pre-programming has a small microchip called the random number generator (this is RNG). Slots machines that have this microchip, guarantee you that every spin of the reel has an equal shot to produce a jackpot.
There are a lot to say abou it, but the final conclusion was given by the Gambling Wisdom of the Week: “Percentages never lie. We built all these hotels on percentages. We stay rich on the percentages. You can lose faith in everything, religion and God, women and love, good and evil, war and peace. You name it. But the percentage will always stand fast.”