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

Casino slots have Random Number Generators (RNG) which are continually generating combinations, even when the machine just isn't being played.

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

The payout percentage controls the amount the slot machine will payout, for example the payout percentage could be 90%, meaning click through the next post slot game will payout 90% of all of the bets played and the casino only gets to keep 10%.

This isn't to state 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 then suddenly go on a hot streak and also you might hit a big jackpot.

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