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) which are continually generating combinations, even when the machine is not being played.
Running concurrently with the RNG of the casino 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 and 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 is 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 you might hit a big jackpot.
The payoff percentages will vary between the different games and some of the most popular casinos, like King Neptunes Casino [http://www.virtual-casino-web.com/king-neptunes-review.html], offer a payout of upto 95%!
So in essence the slot machine takes all the money played into it and pays it out to few lucky winners. The casino only gets to keep a relatively small percentage of all the bets placed.
The casino slot software controls every part of the machine, from the flashing lights to the spinning of the reels.
When you hit spin on the slot machine, a combination is produced by the RNG which corresponds to the pictures on the reel.