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Slot machine

Slot machines in the Trump Taj Mahal
Slot machines in the Trump Taj Mahal

A slot machine (American English), poker machine (Australian English), or fruit machine (British English) is a certain type of gambling machine. Classically, a slot machine is a coin-operated machine with three or more reels that rotate when a lever on the side of the machine is pulled. The machines include a currency detector that validates the coin or money inserted to play. (The slot machine is also known informally as a one-armed bandit because of its appearance.) The machine typically pays off based on patterns of symbols visible on the front of the machine when it stops. Modern computer technology has resulted in many variations on the slot machine concept. Today, slot machines have become one of the most popular attractions in casinos.



The slot machine was invented in 1895 by Charles Fey of San Francisco, California. The first machine, known as Liberty Bell, had pictures of diamonds, hearts, spades, and cracked Liberty Bells on three mechanical reels. Three bells in a row produced the biggest payoff, ten nickels. Liberty Bell was a huge success and spawned a thriving mechanical gaming device industry. Another early machine gave out winning in the form of fruit flavoured chewing gums with pictures of the flavours as symbols on the reels. The popular cherry and melon symbols derive from this machine. The "BAR" symbol now common in slot machines was derived from an early logo of the Bell-Fruit Gum Company. In 1964, Bally developed the first fully electromechanical slot machine called Money Honey.


A row of "Wheel of Fortune" slot machines in a casino in Las Vegas. This specific slot machine is loosely based on the TV game show Wheel of Fortune
A row of "Wheel of Fortune" slot machines in a casino in Las Vegas. This specific slot machine is loosely based on the TV game show Wheel of Fortune

A person playing a slot machine purchases the right to play by inserting coins, cash, a debit card, or in newer machines, a bar-coded paper ticket (known as "ticket in/ticket out" machines), into a designated slot on the machine. The machine is then activated by means of a lever or button, or on newer machines, by pressing a touchscreen on its face. The game itself may or may not involve skill on the player's part -- or it may create the illusion of involving skill without actually being anything else than a game of chance.

The object of the game is to win money from the machine. The game usually involves matching symbols, either on mechanical reels which spin and stop to reveal one or several symbols, or on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, and simple shapes such as bells, diamonds, or hearts.

Most games have a variety of winning combinations of symbols, often posted on the face of the machine. If a player matches a combination according to the rules of the game, the slot machine pays the player cash or some other sort of value, such as extra games.

There are many different kinds of gambling slot machines in places such as Las Vegas. Some of the most popular are the video poker machines, in which players hope to obtain a set of symbols corresponding to a winning poker hand. There are standard 5-card draw machines, all the way up to 100-play machines, where you can play 100 hands at a time.

Becoming more popular now are the 9 line slots. Usually these are themed slots (Addams Family, I Dream of Jeannie, etc.) with a bonus round. Most accept variable amounts of credit to play with 1 to 5 credits per line being typical. The higher the amount bet, the higher the payout will be.

Of course, there are the standard 3 - 5 reel slot machines, of various types. These are the typical "one-armed bandits".

One of the main differences between video slots and reel slots is in the way payouts are calculated. With reel slots, the only way to win the maximum jackpot is to play the maximum number of coins (usually 3, sometimes 4, or even 5 coins per spin). With video slots, the fixed payout values are multiplied by the number of coins per line that are being bet. In other words: on a reel slot, it is to the player's advantage to play with the maximum number of coins available. On video slots, it is recommended to play as many individual lines as possible, but there is no benefit to the player in betting more than one credit per line with regards to calculating the payout amounts. (There are some isolated cases where a video slot machine requires the maximum number of credits per spin to be inserted to win the largest payout, but those are the exception.) An example: On the "Wheel of Fortune" reel slot, the player must play 3 coins per spin to be eligible to trigger the bonus round and possibly win the jackpot. On the Wheel of Fortune video slot, the chances of triggering the bonus round or winning the maximum jackpot are exactly the same regardless of the number of coins bet on each line.

Larger casinos offer slot machines with denominations from $.01 (penny slots) all the way up to $100.00 or more per credit. Large denomination slot machines are usually cordoned off from the rest of the casino into a "High Limit" area, often with a separate team of hosts to cater to the needs of the high-rollers who play there.

In the last few years has been introduced the tokenization: 1 coin (token) buys more than one credit. The benefit to tokenization is that a single slot machine can offer the same game at whatever price level the player would like to play at. The player selects what denomination level (penny, nickel, quarter, dollar) they would like to play from a menu, and the machine will then calculate how many credits they receive for their cash in and display the amount of available credits to the player. This eliminates the need for the player to find a specific denomination of a particular machine; they can concentrate on simply finding the machine and setting the denomination once they decide to play.



The coin hopper is where the coins are held in a slot machine. The hopper is a mechanical device that rotates coins into the casino tray when a player wants his credits/coins (press Cash Out button). Often hoppers are filled to overflowing by players, so they don't only run empty they sometime are overflowing.

Shortpay refers to a payout made by a slot machine, less than the amount indicated by the payout schedule. Occurs when the coin hopper becomes depleted during a payout and the remaining amount is paid to the player by a hand pay.

Hand Pay is when the slot attendant or cage gives the player a cash payout, rather than the actual slot machine paying out from the coin hopper. A hand pay may be automatically requested by the slot machine if the total credits on the machine is greater than 800 coins.

A hopper fill slip is a document used to record the replenishments of the coin in the coin hopper which are required as a result of payouts to players. The slip indicates the amount of coin placed into the hoppers, as well as the signatures of the employees involved in the transaction, the slot machine number and the location and the date.

Weight count is is an American casino term, refering to the dollar amount of chips and tokens removed from a slot machine coin hopper and counted by the caino's hard count team through the use of a weigh scale.

Optimal play is a payback percentage based on a gambler using the optimal strategy in a skill-based slot machine game.

The Theoretical Hold Worksheet is a worksheet provided by the manufacturer for all slot machines which indicates the theoretical percentage that the slot machine should hold based on adequate levels of coin-in. The worksheet also indicates the reel strip settings, number of coins that may be played, the payout schedule, the number of reels and other information descriptive of the particular type of slot machine.

Pay Table

Each machine has a table that lists the number of credits the player will receive if the symbols listed on the pay table line up on the pay line of the machine. Some symbols are wild and will pay if they are visible in any position, even if they are not on the pay line. Especially on older machines, the pay table is listed on the face of the machine, usually above and below the area containing the wheels. Most video machines display the pay table when the player presses a "pay table" button or touches "pay table" on the screen; some have the pay table listed on the cabinet as well.


It is a common belief that the odds on a machine have something to do with the number of each kind of symbol on each reel, but this is not the case. Modern slot machines are computerized, so that the odds are whatever they are programmed to be. For instance, if the jackpot combination is "7-7-7", slot machine owners can fool/tease people by making "7-7-(non-7)" come up frequently. In modern slot machines, the reels and lever are present for historical and entertainment reasons only. The positions the reels will come to rest on are chosen by a computer chip as soon as the lever is pulled or the "Play" button is pressed.

Slot machines are typically programmed to pay out around 82-98% of the money that goes into them as winnings. The winning patterns on slot machines, the amounts they pay, and the frequency at which they appear are carefully selected to yield a certain percentage of the cost of play to the "house" (the operator of the slot machine), while returning the rest to the player during play. Suppose that a certain slot machine costs $1 per spin. It can be calculated that over a sufficiently long period, such as 1,000,000 spins, that the machine will return an average of $950,000 to its players, who have inserted $1,000,000 during that time. In this (simplified) example, the slot machine is said to pay out 95%. The operator keeps the remaining $50,000. The payout percentages are set at the factory when the casino orders the machines. Changing the payout percentages after a slot machine has been placed on the gaming floor requires a physical swap of the game software which is usually stored on an EPROM but may be downloaded to Non-Volatile Random Access Memory (NVRAM) or even stored on CDROM or DVD depending on the technological capabilities of the machine and the regulations in each jurisdiction. In Nevada, the casino is forbidden by law to alter the payout chip. These chips are sealed with a tamper-evident seal and can only be changed by the state Gaming Control Board. Other jurisdictions may have different rules.

Slot machines common in casinos at this time are more complicated. Most allow players to accept their winnings as credits which may be "spent" on additional spins.

Often machines are linked together in a way that allows a group of machines to offer a particularly large prize, or "jackpot". Each slot machine in the group contributes a small amount to this progressive jackpot, which is awarded to a player who gets (for example) a royal flush on a video poker machine, or a specific combination of symbols on a regular or 9 line slot machine. 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 machines may be owned by the machine maker who is responsible for paying the jackpot. The casinos lease the machines rather than owning them out right. Megabucks may be the best known example of this type of machine. Megabucks Nevada starts at $7,000,000 after a jackpot. The new penny Megabucks video game has a jackpot that starts at $10,000,000.

Slot machines that are not linked to a large regional jackpot such as Megabucks usually have better payout percentages, as linked machines have to take into consideration the large jackpot amount into their payout percentage calculations.

American slot machines

In the United States, the public and private availability of slot machines is highly regulated by state governments. Nevada is the only state that has no significant restrictions against slot machines both for public and private use. In New Jersey, slot machines are only allowed in casinos operated in Atlantic City. Several states (Illinois, Indiana, Iowa, Louisiana, Mississippi, and Missouri) allow slot machines (as well as any casino-style gambling) only on licensed riverboats or permanent barges. Native American casinos on reservations cannot have true slot machines unless allowed by the state that the tribal casino is located in (per Indian Gaming Act).

Some states have restrictions on the types of slot machines that can be used in a casino or other gaming area. "Class III" slot machines are machines without restrictions, most often seen in Las Vegas or Atlantic City (commonly referred to as "Vegas-style slots"). Some casinos are in states that require them to use "Class II" slot machines, which usually have a player skill requirement attached. The primary difference between a Class III machine and a Type II machine is that with a Class III machine, a player's chance of winning any payout is the same with every play, and each machine operates independently of each other. A Class II machine mimics bingo or scratch-off lottery tickets in that all the machines are linked to play against each other, pulling a predetermined number of winning combinations from a central database and distributing those to all machines.

For a list of state by state regulations on private slot machine ownership, see Slot machine (U.S. state ownership regulations)

Slot clubs

Many American casinos offer free memberships in "slot clubs", which return a small percentage of the amount of money that is bet in the form of "comps" (complimentary food, drinks, hotel rooms, or merchandise), or sometimes as cash back (sometimes with a restriction that the cash be redeemed at a later date). These clubs require that players use a card that is inserted into the slot machine, to allow the casino to track the player's "action" (how much the player bets and for how long), which is often used to establish a level of play that may make a player eligible for additional comps. Comps or cash back from these clubs can make a significant difference in the maximum theoretical return when playing slot machines over a long period of time.

Australian slot machines

Generally referred to as poker machines or "pokies", but officially known as 'Gaming Machines', Australia has one of the highest concentration of poker machines per head of population in the world, with changes in regulations leading to a profusion of poker machine venues across the country. Various objectors, including many branches of the clergy and also charities for the poor, have criticised the spread of the machines, as they claim that it has led to a huge rise in the levels of "problem gambling" - gambling to a level that causes financial and social stress to the gambler and their families, as well as the general levels of gambling.

Australian-style poker machines use video displays to simulate (usually) five physical reels. These machines also have additional bonusing and second-screen features such as free games and bonus levels. They also allow for multiple lines (up to 50) or multiple ways (up to 243 ways) to be played. This higher level of complexity has meant that greater revenues can be obtained by operators, but also that the potential for problem gambling to develop is increased.

Poker machines are found in casinos (approximately one in each major city) as well as pubs and clubs (usually sports, social, or RSL clubs). This greater accessibililty is also seen as a potential contributor to problem gambling.

The first Australian state to legalise this style of gambling was NSW in 1956 when they were made legal in all registered clubs in the state.

Most problem gamblers attending counselling through Gamblers Help report poker machines as the problematic form of gambling. Due to this there is a significant focus on the regulation of multi hand poker machines, and many groups are advocating for legislative change.

Laws governing gambling in Australia are controlled at the state level and as such, they vary from state to state. In the state of Queensland gaming machines in pubs and clubs must provide a return rate of 60% while machines located in casinos must provide a return rate of 90%.

European slot machines

Slot machines are often known as fruit machines and AWP (Amusement with Prizes) in Britain. Slot machines are commonly found in pubs, clubs, arcades, and some take-away food shops. These machines commonly have 3 or 6 reels with around 16 or 24 fruit symbols printed around them. These reels are spun, and if certain combinations of fruit appear, winnings are paid from the machine, or subgames are played. These are very similar to slot machines seen in casinos and elsewhere around the world, but the term "fruit machine" is usually applied to a type of machine more commonly found in pubs and arcades. These games have lots of extra features, trails and subgames with opportunities to win money, usually more than can be won from just the reels. However, the jackpots from these fruit machines are strictly limited with many machines paying no more than a maximum of £25 in any one win.

It is known for machines to payout multiple jackpots, one after the other, this is known as a streak but each jackpot requires a new game to be played (circumventing the maximum £25 pound per game rule). Private members clubs are allowed "club machines" which have higher jackpots.

These machines also operate in a different fashion to American slot machines; whereas slots are programmed to pay a percentage over the long-run, there is no reason why a jackpot cannot be paid straight after one has already been won - this is because over the long-run the percentage payout will be the same. However, in the UK, a fruit machine takes on an amount above its payout percentage before winning, so if a payout is 95%, a machine will make the player lose £10 before paying out £9.50. As such, it is sensible to watch for people playing these machines but not winning as the likelihood of a win increases. This, however, is called Sharking.

This type of fruit machine is popular across Europe (in the countries where they are legal), and very popular in countries such as the Czech Republic, Russia, and Ukraine.

The minimum payout percentage is 70% in Britain, with pubs often setting the payout at around 78%.

It has been alleged by the Fairplay campaign that UK fruit machines employ fraudulent techniques in which gambles and chances which appear to be random are in fact pre-determined 1 and cannot be affected by player choices. 2

...at this point, you'll have gambled the win up to £25. However, the machine doesn't want you to gamble any further. If from the 5 you select "High", the machine will spin in a 3 and you'll lose. If, on the other hand, you select "Low", the machine will spin in a 9 and you'll lose...

The claims centre around the emulation of fruit machine hardware on computers, which allow for the machines RAM state to be saved at a particular point and replayed making a different choice. The fruit machine industry has hit back 3 at the allegations 4. Currently the issue has supposedly been considered by the Uk Gaming Board (now the Gambling Comission) and warning notices and possibly modifications are to be put in place 5, though it is unclear as to whether this has happened. As the Fairplay site has not been updated in over a year, the current situation is unknown 6

Japanese slot machines

Japan has has a relatively new history in slot machines, roughly since after the American occupation during the World War II era.

The machines are regulated with IC chips, and has six different levels changing the odds of a "777". The levels provide a rough outcome of between 90% to an astonishing 160% (200% if using skills). Indeed, the Japanese slot machines are "beatable".

Despite the many varieties of the machines, there are certain rules and regulations put forward by a commission. For example, there must be three reels. Also, all reels must be accompanied by buttons which stop these reels, etc.

Myths debunked

  • Standard slot machines do not get "hot" or "cold". The chances of hitting a winning combination are exactly the same with every spin.
    • (Exception: UK-style AWP machines are progressive which means chances of winning will increase over time if the machine has not paid any wins out. Many also "force" wins on players in order to meet the payout percentage)
  • Except possibly in a few jurisdictions, slot machines are never "due to be hit" if they haven't paid out a jackpot in a while.
  • There is a science to the placement of slot machines on the gaming floor, but the highest paying machines are not necessarily placed in high-traffic areas. Typically, machines of similar payback percentages are grouped together, with 1% or less difference from machine to machine in the group.
  • Using your slot club card does not affect the machine's payout percentage.
  • In most jurisdictions, casinos cannot alter the machine's percentages by time of day, day of week, or remotely via a computer. Changing the percentage payouts on these machines is an involved process of physically replacing parts inside the machine, and can't be done without regulatory oversight.
    • (Exception 1: UK-style AWP machines can have their percentage easily altered via a percentage key (inserted onto the machines motherboard) or by the setting of dip switches. There is no requirement for this to be supervised or reported in the UK.)
    • (Exception 2: In many markets where central monitoring and control systems are used to link machines for auditing and security purposes, usually in wide area networks of multiple venues and thousands of machines, player return must usually be changed from a central computer rather than at each individual machine. A range of percentages are preprogrammed into the game software and selected by configuring the machine remotely.)


  • Slot machines, like other gambling devices and games, can be addictive to some individuals.


  • The first Liberty Bell slot machine can be found at the Liberty Belle Saloon & Restaurant on 4250 S. Virginia, Reno, Nevada.

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