Generator Of Random Numbers
There are many modern computerized slot machines. They programme the odds. In modern slot machines, the reels and lever exist only for historical and entertainment reasons. The positions of the reels depend on a Random Number Generator. It is included into the machine's software.
Random numbers are constantly generated by the RNG 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. A fraction of a second earlier or later, and the result would be different.
The numbers generated by the RNG seem to be not exactly random. Indeed, most RNGs will eventually repeat their number sequence. The cause of it is in poor programming. It is relatively easy to build pseudo RNGs with very long periods. A single period can't be completed by any computer in the expected lifetime of the universe. It was Ronald Dale Harris, a former slot machine programmer, who knew the pseudo RNG code and seed values. Specific gambling games equations were discovered by him. Thanks to them the fact that the next set of selected numbers would be based on the previous games became known. However even if nobody uses the machine the RNG continues to pick numbers. So you can't find an exact place of a number in the sequence.

Payout Percentage
Winnings 82–98 per cent of the money that is wagered by players are typically paid out by slot machines. This is known as the theoretical payout percentage. The minimum theoretical payout percentage is controlled by jurisdictions. Law or regulation are used to establish it. Nearly each casino has its own winning pattern. The amounts they pay and the frequencies of these pay-outs are reflected in it. 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 is given back to the players.
A slot machine's theoretical payout percentage is set at the factory when the software is written. Changing the payout percentage requires a physical swap of the software. As it is a time-consuming process it is done infrequently. There is sometimes a tamper-evident seal on the EPROM. To change it Gaming Control Board officials should be present. Other jurisdictions constantly ensure that slot machines 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. After the change is made, 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.

Machines That Are Linked
Linking the machines in a special way is made to offer a particularly large prize, or jackpot. If a player gets a specific combination of symbols the progressive jackpot from this group of machines is given to him. 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. The machines are then owned by the manufacturer, who is responsible for paying the jackpot.

Near-miss
The reel display of modern slot machines is under computer software's control. It is possible to make the slot machine frequently display combinations that are close to winning combinations.
This practice is called near-miss programming.
There is a related phenomenon which is also called near-miss. Winning percentages programmed into the slot machine 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. There are roughly equally randomly distributed combinations above and below the pay line. Only if abbreviated physical reels are used to display a win pattern based upon the RNG this can occur. In video slot machines the symbols that appear around the winning line are usually an accurate depiction of how the reels were mathematically modeled.
There was an investigation held by the Nevada Gaming Commission concerning the issue of a near-miss above or below the pay line. So long as the near-miss above or below the pay line was not specially programmed it was recognized legal. In other words, any other combination must be just as likely to occur as the near-miss. The machine cannot be specially programmed to show winning combinations more frequently than other combinations above or below the pay line.
Australia also forbids to use near-miss programming, where a near miss is inaccurately displayed. Due to this, regulators use stop motion cameras to audit manufacturer's practices.

Fraud
Mechanical slot machines and their coin acceptors were sometimes considered to be cheating devices and other scams.
Coin acceptors have become obsolete in favor of bill acceptors and modern slot machines are controlled by EPROM computer chips. It is difficult to defraud these machines because they their bill acceptors are designed with advanced anti-cheating and anti-counterfeiting measures. Nowadays microwaves are used to defraud slot machines.