Slot machines or commonly referred as slots but also fruit machines etc. are well-known casino machines that create a game based on luck for the players. The game it’s the most popular in the live and online casinos around the world. It makes up around 70% of the Las Vegas industry. The classical version included a machine with a screen that features three or more wheels with designed symbols on it that spin. There was a lever that needed to be pulled in order for the slot mechanism to start and that’s why sometimes slots were called in a pejorative way as “one arm bandit”. The payout is made according to the patterns of the symbols displayed on the wheels. We have talked extensively, on our Betzest blog, about free slots and real money slots and their modus operandi, and in this article, we will highlight some important historic aspects of slots and how slots evolved to the present day technological developments. The term slot machine it’s related to the slot cavity in the machine were the coins are inserted, while the name fruit machine is related to the classical slots machines spinning symbols which used to be fruits like lemons, cherries, grape but also sevens and bells.

A Brief History of Slots

The precursor of the modern slot machine was a poker machine which contained five drums holding 50 poker cards and the players would insert coins, pull the lever and hope for a good hand of poker. It was developed in 1891 by Sittman and Pitt in Brooklyn, New York. The pay outs were usually beers and cigars and this machine proved to be very popular among bar frequenters. Two cards were removed from the deck in order to create the house edge and give less chances to players to win. The machine was still primitive and wasn’t able to offer payouts for every winning combination and that was until 1895 when Charles Fey from San Francisco introduced the first slot machine. The machine had three spinning reels and in total six symbols, the playing card symbols, a horseshoe and a bell. The slot was named Liberty Bell and the highest winning combination was a three aligned bells. The slot machine got so popular in bars and saloons that Fey couldn’t keep up with the high demand. Many other manufacturers started to copy the Bell’s machines and the slot game was highly commercialized. Many other machines were developed later using the same model with symbols ranging from patriotic symbols to fruits, as mentioned above.


It was only in the early 1960’s that the first electro-mechanic slot was introduced and the innovation was the automatic payout up to 500 coins. The machine was called Money Honey and had the lights, sounds and noise typical of Las Vegas. This slot machine was activated with the famous lever and there wasn’t a need for a slot attendant. The first video slot was introduced in 1976 In Las Vegas. The technology was bought by IGT later while the first video slot to offer a second scree bonus round was introduced in 1994 in Australia. Initially casino managers put slot games at the entrance of the casino floor for diversification. Real money slots don’t require any particular knowledge and they were very appealing to non-calculative gamblers which they don’t like classic games like black jack or roulette. But soon slots got the bigger piece of the pie and as mentioned earlier they can make up to 70% of the revenue share in Las Vegas. Over the years the slots technology has improved and the classical levers and pulls are substituted by computer generated random numbers and mechanisms but the core game has remained essentially the same. The payout lines are also the main difference between classic slots and the video slots. Multiline payout slots are introduced after the 90’s, and the winning combinations are not like the classic slots in which there are maximum three or five wining horizontal combinations. In video slots there can be as much as 1024 pay lines and the higher the bet the higher the winning amount. Slots and video slots are also famous for their endless themes, which contributes greatly to their huge success. Themes can vary from fruits, gems, stars, animals, iconic characters, movies and popular culture as well.

Slots Operation and Technology

Most modern video slots are designed similarly to the classical models but their modus operandi it’s different. Basically in modern live casino and online slots there aren’t stops, notches and springs but there is a computer who tells the reels where to stop. The random number generator that is at the core of this system ensures that each symbol of the reels has an equal chance of coming out and hitting the jackpot for instance. This is of course an advantage for the players and the manufacturers. For the players this is an insurance that the game is fair and for the manufacturers it’s easy to program how often and in what amounts the machine will pay. Slot games are also designed very carefully in order to achieve a certain payback percentage ad that’s called the RTP.

We have talked extensively about this mechanism in our blog but we can mention here that this is the percentage that the casino wins over a certain period of time. So for an RTP of 97%, the machine will give back 97 € for each 100€ played. There is of course a minimum for the slot RTP and it’s about 75% but in general in the top online casino it ranges between 94% to 97% depending on the slot. The casino is completely prohibited to change those RTP’s and contrary to popular opinion there is absolutely no way for a serious and regulated casino to manipulate a slot. The RTP’ rates are carefully designed and tested by game mathematicians and they are embedded in the game code. The probability of each hand coming is also of interest regarding slot machines.

The pay tables have a series of hands and their probability of coming can range from 1 to 4000 at average. Developers keep those probabilities info guarded and they publicly release only the theoretical payback percentage or the RTP. Also there aren’t hot or cold slot machines as they say. Every time you hit the spin button or pull the lever there is exactly the same chance to hit the biggest winning hand as the computer generated images are completely random and based on chance. Random number generators are constantly producing sequences of random numbers and the result of the game depends completely on the moment that the players hits the spin button. A second earlier or a second later the result of the game would have been completely different. Moreover, the RNG generates numbers even when the machine it’s not being played on so the prediction of the outcomes of the games by players or other computers it’s practically impossible.

In all the modern slots and video slots the payout lines, reels and betting options are selectable according to each player’s choosing, and they can choose to play minimum bet with a single winning line or they can choose to play more winnings lines with more chances to win of course. It is well known that regardless the payout lines, if the player has to play in a maximum bet if he wants to reach the maximum jackpot hand and take away the big win. In the progressive jackpot slots, however, the jackpot increases steadily as long as players are putting money on the linked slots and in many casinos it isn’t necessary to bet the max value to win it. The variations of the slot games and video slot games, are mostly visual and thematic. Many of them vary in game play as well or the bonus option structures like wilds, scatters, multipliers etc. but the mechanism remains the same in all of them. Video slots were confronted with general distrust when they first came out as the players were used to spinning reels and many of them had the perception of the games being manipulated somehow but this was proven false as the mechanisms were made transparent and in many modern live casino slots the pulling lever it’s added just aesthetically. Betting denominates are also variable and they range from 0.15€ per spin to 400€ per spin. The later are high limit machines and the payouts can go as much as 500K € per single spin.

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Slot Terminology

Bonus rounds are special rounds within the video slot activated with a special symbol combination and they give the chance to the player to choose between multiple symbols that hide special payouts that are awarded to the player. Many of the bonus rounds are special phases of the free spins rounds and they can be also collected as coin credits and saved to be used at a later phase. Also they are also known as Pick and Click Bonus

Candles are the lights in the top of the slot machine that signal to the attendants if the customer wants to change cash or to cash out.

The credit meter is the part that displays the remaining balance of the player on the slot.

Free Spins are the most popular form of bonus play and they are free of charge spins that are usually activated by a combination of three or more scatter symbols

Pay lines are lines that go through the symbols on the reels from left to right and sometimes from right to left as well and they evaluate if a combination is winning or not. Classical slots as mentioned above have one to maximum nine pay lines while video slots have up to 1024 different paying combinations.

A roll up is referred to the sounds and the lights that the slot game makes during a huge payout.

A scatter is a special symbol that activates bonus rounds usually free spins. In general, it is required three or more scatters to activate the free spins or the bonus rounds in a slot game.

Volatility or sometimes called the variance its related to how often and in what amounts a slot machine will pay. Low volatility means that the slot will pay quite often but in small amounts while high volatility means that the slot will pay rarely but in higher sums.

Wilds are referred to substituting symbols like the joker in video poker for instance. They substitute other symbols on each reels and three of a kind together with a wild it’s automatically a four of a kind.

Multiplier is referred to the multiplication option that is given to the player during free sins. If free spin with an x5 multiplier means that all the winnings from that sessions of frees pins

Re-spins are essentially like bonus rounds and the reels continue to roll until there is a winning combination.