Slot machines, also known as a fruit machines (e.g., in the United Kingdom), pokies (e.g., in Australia), one-armed banditsSlot machines, also known as a fruit machines (e.g., in the United Kingdom), pokies (e.g., in Australia), one-armed bandits, or simply slots, are games of... More, or simply slots, are games of chance typically found in casinos and sometimes bars or other establishments. Players insert coins, tokens, or digital credits to play. The machine features a series of reels adorned with symbols that spin and stop, determining the outcome. A win is achieved when specific combinations of symbols align in a sequence called a payline. Modern variations may include multiple paylines, bonus games, and progressive jackpots. The machine’s design often incorporates bright graphics, music, and sound effects to enhance the gaming experience.
Historically the outcome of each reel was mechanical and (with a fair machine) was designed so that each outcome was equally likely and outcomes one on reel or one spin were independent from outcomes on another reel or on previous spins. The randomness of today’s slot machines, however, is determined by a computer chip, a so-called “virtual reel”, that maps the likelihood for each physical reel (or potentially for combinations of outcomes on the physical reel) to any desired probability. The virtual reel allows for near misses on the physical reel to occur far more often than the surface-level structure would suggest and it allows for jackpots that would not otherwise be possible. Indeed, outcomes need not (or must not) be independent from one spin to the next depending on the jurisdiction.
History of the Slot Machine: From Mechanical to Digital
Mechanical Slot Machines
The slot machine has its roots in the late 19th century. The precursor to the modern slot machine was developed by Sittman and Pitt of Brooklyn, New York, in 1891. Their creation was based on poker and used 50 playing cards on five spinning drums. Players would insert a nickel and pull a lever, and the machine would deal out a poker hand. There were no direct payout mechanisms initially, so winning hands might earn a player a free beer or a cigar from the bar where the machine was located.
The first true slot machine that more closely resembles those we’re familiar with today was invented by Charles Fey of San Francisco at the end of the 19th century. Named the “Liberty Bell,” Fey’s creation had three spinning reels with symbols like horseshoes, diamonds, spades, hearts, and a cracked Liberty Bell. A spin resulting in three Liberty Bells in a row produced the highest payout. Fey’s machine also introduced the simpler and more effective mechanism for automatic payouts, laying the foundation for future slot machine designs.
The Liberty Bell and other mechanical slot machines were relatively straight forward in that the probability for each outcome could be calculated with basic knowledge of probability theory and the various payouts selected so that the total expected valueExpected value or EV is the average return one can expect to get from a repeated decision, such as from a gamble, if it is... of the game was in favor of the proprietor. For example, if the machine had three reels, each with 20 different symbols, and the reels were “fair” in the sense that they were designed with an equal probability of landing on any symbol, the probability for any one 3-symbol combination would be 1 over 203, or 1/8000. If it cost 5 cents to play the game then the sum of the products of each prize times 1/8000 needed to equal less than 5 cents for the machine to offer an expected gain to its owner.
Left: The “Liberty Bell,” the father of the contemporary slot machine (image courtesy of Marshall Fey).
Right: A contemporary 25¢ banking slot machine with a siren light on top (image courtesy of Paul and Sarah Gorman)
From: Bennis, W. M., Katsikopoulos, K. V., Goldstein, D. G., Dieckmann, A., & Berg, N. (2012). Designed to fit minds: Institutions and ecological rationalityCoherence versus Correspondence In decision science, the terms "coherence" and "correspondence" refer to two different criteria for evaluating the quality or correctness of, beliefs, judgments,.... In P. M. Todd, G. Gigerenzer & the ABC Research Group (Eds.), Ecological Rationality: Intelligence in the World. New York: Oxford University Press.
As the 20th century progressed, slot machines evolved in design and function. In the 1960s, Bally Manufacturing developed the first fully electromechanical slot machine named “Money Honey.” This was significant as it began to phase out the typical mechanical components, relying more on electronic processes for operation. The introduction of this machine marked the beginning of a transition from purely mechanical operations to electronically-augmented mechanisms.
The true digital revolution for slot machines came in the 1970s. In 1976, the first video slot machine was developed by the Las Vegas-based company Fortune Coin. Using a modified 19-inch Sony TV for the display, it was the pioneer in combining video technology with slot play. However, the introduction of computer chips to slots was a game-changer. These chips allowed for the programming of “virtual reels,” a mapping between each symbol on the reel to essentially any likelihood imaginable, making it possible for certain outcomes to be far less likely than others and for the likelihoods to be so low that jackpots could be in the millions of dollars. This created a disconnect between the surface structure of the game, which appeared to function like traditional mechanical slot machines with the impression that outcome probabilities and expected value could be calculated, on the one hand, and a hidden structure that players could only guess at from experience playing.
One of the most pernicious aspects of the disconnect between the physical reel and the virtual reel was the facilitation of the near missThe term "near miss" could be used in any domain where a particularly good (or bad) outcome has—or seems to have—almost occurred. Near misses are... whereby the blank stops just above and below a jackpot symbol could be programmed on the virtual reel to occur more often than other stops, or the jackpot symbols can be programmed to occur more often on early reels, creating the false appearance of a near miss.
The digitization of slot machines allowed for the introduction of a vast array of new game features, bonus rounds, the banking of credits, cumulative jackpots, multi-line playing, etc. By the 1980s, these computerized video slots started to proliferate across casinos, paving the way for the advanced and feature-rich games we see today. Indeed, most of today’s slot machines have shed the pretense of the mechanical wheel altogether and use animated video displays, though they still display the spinning of the reels and often have a lever that can be pulled, suggesting falsely that the symbol outcomes are based on a random selection among stops on each reel that are activated mechanically by pulling on the lever. They often show as many as five reels and three or more lines of play and allow the gambler to bet multiple credits that activate different combinations of the lines, including diagonals or zigzags, so that with the maximum number of coins bet many games pay a prize almost every spin, just a lower prize than the total number of coins bet. Today jackpots often result in the printing of a ticket rather than actual monetary payouts and the digital sound of coins dropping replacing actual coins dropping, with bells and sirens announcing large jackpots to the entire casino from among hundreds or thousands of slot machines in the larger casinos, conveying a sense that large jackpots are being paid out regularly, which in fact is the case. Just not regularly at any one machine.