Modern casino slots are controlled by computer chips and software, and the win percentages are preprogrammed into the software.

Casino slots have Random Number Generators (RNG) that are continually generating combinations, regardless of whether the machine is not being played.

Running concurrently with the RNG of the casino fantastic online slot machine is the payout percentage.

The payout percentage controls how much the slot machine will payout, for example the payout percentage might be 90%, meaning the slot game will payout 90% of all the bets played as well as the casino only gets to keep 10%.

This is not to say that every time you bet 10 credits you will receive 9 in return - where will be the fun and excitement in that? Instead the casino slot machine game will not pay out for a while, and after that suddenly go on a hot streak and also you might hit a big jackpot.

So in essence the slot machine takes all the money played into it and pays it out to few lucky winners.