The RNG
Nowadays slot machines are computerized. They programme the odds. In modern slot machines, the reels and lever exist only for historical and entertainment reasons. It is a Random Number Generator that chooses the reels positions. The machine's software contains it.
Random numbers are constantly generated by the RNG at an extremely high rate. When a player presses the Play button the most recent random number determines the result. This means that the result varies depending on exactly when the game is played. The result would be different a fraction of a second earlier or later.
The numbers generated by the RNG seem to be not exactly random. Indeed, most RNGs will eventually repeat their number sequence. Poor programming is its reason. It is relatively easy to build pseudo RNGs with very long periods. The computer that is able to complete a single period in the expected lifetime of the universe hasn't been invented yet. The access to the pseudo RNG code and seed values was known to Ronald Dale Harris, a former slot machine programmer. He discovered equations for specific gambling games like Keno. 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.

Percentage Of The Payout
Slot machines are typically programmed to pay out as winnings 82–98 per cent of the money that is wagered by players. The term theoretical payout percentage is used to denote it. Jurisdictions influence the minimum theoretical payout percentage. Law or regulation typically establish it. There is a certain winning pattern nearly in every casino. 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 goes to the players.
When a slot machine's software is written its theoretical payout percentage is also set. Changing the payout percentage 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. Only Gaming Control Board officials can change it. 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. 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 That Are Linked
Offering of a particularly large prize, or jackpot becomes possible when a group of machines is linked in a special way. 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.
Multiple machines can be sometimes 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 controlled by computer software. 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.
A related phenomenon is sometimes 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. 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.
There was an investigation held by the Nevada Gaming Commission concerning the issue of a near-miss above or below the pay line. 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. Winning combinations aren't supposed to be shown 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 susceptible to cheating devices and other scams.
Modern slot machines are controlled by EPROM computer chips and coin acceptors were changed for bill acceptors. These machines and their bill acceptors are designed with advanced anti-cheating and anti-counterfeiting measures and are difficult to defraud. Nowadays microwaves are used to defraud slot machines.

Here is the list of the most amusing myths concerning slots.
You can spot a winning slot machine.
The only way you'll spot a winning slot machine is when the bells are ringing and the money is dropping. Slot machines use random numbergenerator and that's exactly that. Random.
Casinos place loose slots near the cashier, aisle ways, etc.
If this were true, it would be the only machines anyone would play. A casino mixes slots all over the casino floor. No one with any experience at playing slots would make a statement like this.
Count the number of symbols on the reels to determine your odds.
It is a rude mistake. RNG decides when the machine will stop and there are thousands of combination available on a 3 reel slot machine.
Casinos can tighten or loosen slot machines from the back office.
In order to change how a slot willpay out is by changing the computer chip. No casino can just flip a switch.
A slot machine that has not been paying is due to hit.
It is not so. With every game the chances of winning are the same.
Pulling the slot machine handle produces more wins than pressing the spin button and visa versa.
It is also a mistake. These things are only mechanisms for beginning the game. The machine knows whether you win or lose before the symbols begin to stop.
Playing with hot coins improves your chances.
Once again, the computer determines a win or loss and the temperature of the machine or moneyirrelevant. Although it's funny that people still burn their fingers with lighters believing this works.
Casinos set slot machines to payback more on the weekends.
One more rude mistake. The chances and odds are always the same. It doesn’t matter when you play.

Slots are one of the oldest casino entertainments. Throughout the years, designs and implementation of slot machines went from mechanical to electronic, and from electronic to digital, then from digital to purely software, but the principles are still the same: the slot machine has reels which spin and, if the pre-defined winning combination plays out, you win. The player inserts coins in the machine and then wins or loses according to the outcome of the game.
In fact all slot machines are the same. They only differ in some peculiarities: odds, payouts, payout percentage and symbols. There are so many varying designs around the classic slot machine that everyone could probably find their own ultimate preferred flavour.
The main difference is the number of lines. Slot machines can be either single line or multilane. In single line slots, the machine has just one line of reels, usually with 4 or 5 wheels, while in multiline there are a number of reel lines. Multi line slots are a little bit more complicated because winning combinations may play out across a number of lines; when you win, the machine will draw you how the symbols combine together and calculate the win automatically. Sometimes you don't win anything at all, and sometimes multiple combinations award you with relatively big winning money. Paylines can be different. They can be vertical, diagonal, zigzags and what not.
Another interesting variation of the slot machine is a jackpot. If the slot machine has a jackpot it means that a certain amount of each additional bet is added to the jackpot. So the jackpot becomes bigger and bigger with every bet. Jackpots can reach several hundreds of thousands dollars. A certain winning combination hits the jackpot, and the lucky gambler collects everything that the ones before him left behind.
Since slot machines appeared they have been played with coins. The new invention is a slot machine online, which doesn’t differ greatly from regular slot machines. Like regular slots they have betting limits, which can be even lower than in real casinos. Unlike the table games, slot machines don't involve any decision on the player's part and so aren't threatened by game management systems because of their fixed odds; the bet limits are more of a traditional thing than anything else.
Software slot machines (as well as the digital ones) are equipped with a random number generator which is what actually plays the game. This methodic allows very fair and precise balancing without actually hurting neither the players' interests nor the casino revenue.

The USA
In the United States the availability of slot machines is highly regulated by state governments. Many states have established gaming control boards to regulate the possession and use of slot machines. There are no significant restrictions against slot machines in Nevada. In New Jersey only hotel casinos operated in Atlantic City are allowed to have slot machines. There are states that allow slot machines only on licensed riverboats or permanently-anchored barges. Only three horse tracks are allowed to have slot machines in Delaware. There is State lottery commission to regulate them.

Casinos: Native American
Slot machines are forbidden in Native American casinos located in reservations. When the tribe first reaches a pact with the state in which it is located it gets the permission to have them. The state is entitled to receive a fraction of the gross revenue from slot machines by the pact.

Slot Machine Classes
There is no federal law governing slot machines. There is no universal classification for all states. There are restrictions on the type of slot machines that can be used in a casino or other gaming area in some states. "Class III" (or "traditional") slot machines operate independently from a centralized computer system. The chance of winning any payout is the same with every play. You can find Class III slots in Nevada or Atlantic City more frequently. "Vegas-style slots" is another name for them.
"Class II" slot machines ("video lottery terminals" or "VLTs") are connected to a centralized computer system. The outcome of each wager is determined by it. Each machine has an equal chance of winning a series of limited prizes. The casino pays a fee to the state for each Class III game. Class II games are not so tightly regulated by the state.

Characteristics Of Class II Games
The player is playing against other players. There is a common prize for which they are competing. Each game has a winner. The game is continued until someone wins. There is a certain number of wins and losses in a given set of wins. The combimation can occur again only after a new batch is initiated. One game is dependent on previous games. The player must be an active participant. All players play from the same set of numbers as the numbers are announced.

Characteristics Of Class III Games
The player is playing against the house. There is no connection between the previous and the next games. Any game has any possible outcome.

Slot Clubs
There is free memberships in "slot clubs" in many casinos of America. A small fraction of the amount of money that is bet is returned in the form of comps. The requirement of such clubs is the usage of cards for the slot machines. Comps or "cash back" allows to make the differences in the maximum theoretical returns significant.

Slots In Australia
Queen of the Nile (manufactured by Aristocrat) is one of the most popular Australian poker machine games. Slot machines in Australia are officially termed Gaming Machines. In Australian-style gaming machines video displays are used to simulate physical reels. There are usually five of them. The use of gaming machines in Australia is regulated by the laws.
Gaming machines are found in casinos as well as pubs and clubs in some states. The first Australian state to legalize this style of gambling was New South Wales. In 1956 they were made legal in all registered clubs in the state.
Only particular forms of gaming machine are permitted to be used in Western Australia.

Britain
Fruit machines, one-armed bandits and AWP are the names for slot machines in Britain. There are fruit machines in pubs, clubs, arcades, and some take-away food shops. There can be 3, 4 or 6 reels with around 16 or 24 fruit symbols printed around them. These reels are spun. The machine pays winnings if certain combinations of fruit appear. There is similarity between these machines and slot machines seen in casinos and elsewhere around the world. But some extra features can be found. The jackpots from these machines are limited. There are some features of fruit machines in the UK. A player may be given the opportunity to hold one or more reels before spinning. It sometimes increases the chance of winning. A finite number nudges following a spin can be also given to a player. A single-step rotation of a reel of the player's choice is a called a nudge.
The maximum payout for an individual game depends on the type and the location of the machine. Private members' clubs have "club machines". They have higher jackpots and are allowed to charge more per game.
These machines also operate in a different manner to American slot machines. The jackpot can be won in each game independently.
The AWP fruit machine is popular across Europe and in countries such as the Czech Republic, Russia, and Ukraine.

Slots In Japan
The term pachisuro is used to denote Japanese slot machines. They originate from the traditional Japanese pachinko game. Slot machines are a fairly new phenomenon. There are slot machines in pachinko parlors and the adult sections of amusement arcades, known as game centers.
The machines are regulated with IC chips. They have six different levels changing the odds of a "777". All machine varieties have certain rules and regulations.

There are many types of slot machine configurations but all work according to the same principles - put the money in the slots and pull the handle! According to the main slot classification there are two types of slots. They are straight slots and progressive slots. The main feature, which distinguishes straight slots from other types is that you get paid according to the payout table, which is shown on the slot machine. There are four other types inside of the straight slot group: multiplier, bonus multiplier, multiple payline and buy-a-pay slots. The Bonus Multiplier game offers a bonus if you make maximum bets. When playing multiple payline slots remember that the number of coins being bet determines the winning amount. The Buy-a-Pay slots are profitable only if you place maximum bets. Progressive Jackpot is the main characteristic of the progressive slots. Progressive jackpot grows with each coin being bet. The amount of the Progressive jackpot is always shown on the slot.