The RNG
Nowadays slot machines are computerized. The odds are programmed. The reels and lever are present for historical and entertainment reasons only. A Random Number Generator determines the positions of the reels. The machine's software contains it.
The RNG generates random numbers at an extremely high rate. When you pres the Play button the result is determined by the most recent random number. That means that the result depends on exactly when the game is played. The result is different every fraction of a second.
It was noticed that the RNG does not actually generate random numbers. The sequence of numbers is repeated by most of the RNGs. Poor programming is its reason. It is relatively easy to build pseudo RNGs with very long periods. There is no computer that is able to complete a single period in the expected lifetime of the universe. The access to the pseudo RNG code and seed values was known to Ronald Dale Harris, a former slot machine programmer. Equations for specific gambling games like Keno were discovered by him. Then the prediction was made that the next set of selected numbers would be based on the previous games played. But the RNG picks numbers even when the machine is not being played. So you can't find an exact place of a number in the sequence.

Percentage Of The Payout
Slot machines usually pay out as winnings 82–98 per cent of the money that is wagered by players. This is known as the theoretical payout percentage. Jurisdictions influence the minimum theoretical payout percentage. Law or regulation typically establish it. Nearly each casino has its own winning pattern. It concerns the amounts they pay and the frequencies of these pay-outs. The winning patterns on slot machines are carefully selected to yield a certain fraction of the money played to the house. The rest of the money goes to the players.
When a slot machine's software is written its theoretical payout percentage is also set. Changing the payout percentage after a slot machine has been placed on the gaming floor requires a physical swap of the software. It is done infrequently because this is a time-consuming process. Certain jurisdictions presuppose the EPROM to have a tamper-evident seal. To change it Gaming Control Board officials should be present. According to other jurisdictions slot machines are randomly audited to ensure that they contain only approved software.
Thanks to the newly developed technology the game, the odds, and the payouts would be able to be changed by the casino's slot manager remotely. Only after the selected machine has been idle for at least four minutes can the change be done. The machine must be locked to new players for four minutes and display an on-screen message informing potential players that a change is being made after the change is made.

Machines Linking
A group of machines offers a particularly large prize, or jackpot if they are linked together in a special way. A small amount is contributed by each machine in the group to this progressive jackpot which is given to a player who gets a specific combination of symbols. The amount paid for the progressive jackpot is usually far higher than any single slot machine could pay on its own.
In some cases multiple machines are linked across multiple casinos. In these cases the manufacturer owning these machines is responsible for paying the jackpot.

Near-miss Programming
The reel display of modern slot machines is under computer software's control. That is why the slot machine can be programmed to display combinations that are close to winning combinations.
The term near-miss programming is used to denote this practice.
There is a related phenomenon which is also called near-miss. It is winning percentages that control the chance of a winning combination appearing on a pay line. However, the combinations appearing above and below the pay line are all roughly equally randomly distributed. This means it is much more likely that a winning combination will appear above or below a pay line than on the pay line. The occurance of this phenomenon is possible when abbreviated physical reels are used to display a win pattern based upon the RNG. Video slot machines have virtual reels and the symbols that appear around the winning line are usually an accurate depiction of how the reels were mathematically modeled.
The issue of a near-miss above or below the pay line was also the subject of the Nevada Gaming Commission investigation. It was considered to be legal as long as the near-miss above or below the pay line was not specially programmed. That means that the possibility of near-miss occurrence should be equal to the possibility of any other combination. The machine cannot be specially programmed to show winning combinations more frequently than other combinations above or below the pay line.
In Australia near-miss programming, where a near miss is inaccurately displayed is not allowed either. Due to this, regulators use stop motion cameras to audit manufacturer's practices.

Fraud
Mechanical slot machines and their coin acceptors were sometimes susceptible to cheating devices and other scams.
EPROM computer chips controls modern slot machines and coin acceptors have become obsolete in favor of bill acceptors. Different advanced anti-cheating and anti-counterfeiting measures have been taken to make it difficult to defraud these machines. One of the recent attempts at defrauding slot machines is directing microwaves toward it to disrupt its proper functioning.

As you know there are different types of slot machines. And do you know that there are even types of slot palyers.
The first type is a persistent player.
The players of this type believe that very soon there will be a period when the machine begins to pay. Any second now the slot machine will roll over and all the coins will be flying out and you will be rich.
The player will play until the machine pays out. He must have found a machine that haven’t paid for a long period of time or he has inserted to many coins and has got nothing. They believe that at least any payout is due to happen. They can’t leave the machine because as soon as they do it will burst forth and pay out large sums. Makes sense if you have lost 0. 00 and have yet to win. The machine will pay any way.
In the old days when a payout occurred players would feel the coins to see if they were hot or cold. If the coins where hot then the slot machine had not paid out in a while and to the chaser this was good as the machine was do. In fact the coins could be hot only because of the numerous lights that heated the coins.
The chaser.
The player thinks that the machine he is going to play is not a machine that never pays. Players feel more comfortable and confident because they have been reinforced with a win and gain trust in the machine. A sense of comfort exists between the slot machine and the player.