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

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

Running concurrently with the RNG of the casino safe online slot gambling site machine is the payout percentage.

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

This isn't to say that every time you bet 10 credits you shall get 9 in return - where is 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 you might hit a big jackpot.