slot machine (American), fruit machine (British), or poker machine (Australian) is a casino gambling machine with three or more reels which spin when a button is pushed. Slots are also known as one-armed bandits because slot machines were originally operated by a lever on the side of the machine (the one arm) instead of a button on the front panel, and because of their ability to leave the gamer penniless. Many modern machines still have a legacy lever in addition to the button.

Slot machines include a currency detector that validates the coin or money inserted to play. The machine 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. Slot machines are the most popular gambling method in casinos and constitute about 70 percent of the average casino's income.[1] It is estimated that thirty percent or more of the profits from gambling machines come from problem gamblers

History
Sittman and Pitt of Brooklyn, New York, U.S. developed a gambling machine which was a precursor to the modern slot machine. It contained five drums holding a total of 50 card faces and was based on poker. This machine proved extremely popular and soon many bars in the city had one or more of the machines bar-side. Players would insert a nickel and pull a lever, which would spin the drums and the cards they held, the player hoping for a good poker hand. There was no direct payout mechanism, so a pair of kings might get the player a free beer, whereas a royal flush could pay out cigars or drinks, the prizes wholly dependent on what was on offer at the local establishment. To make the odds better for the house, two cards were typically removed from the deck: the ten of spades and the jack of hearts, which cut the odds of winning a royal flush by half. The drums could also be re-arranged to further reduce a player's chance of winning.


Description
A person playing a slot machine purchases the right to play by inserting coins, cash, or in newer Ticket-In, Ticket-Out machines, a bar-coded paper ticket, 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 while only being 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 that spin and stop to reveal one or several symbols, or on simulated reels shown on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, numerals or letters, and simple shapes such as bells, diamonds, or hearts; newer video-based machines use animated cartoon characters and images of popular actors or singers


Virtual Reels
Old mechanical slot machines had a set number of reels containing a set number of symbols, each equally likely to appear on the payline after each spin. In the 1980s, however, slots makers incorporated electronics into their products and programmed them to weigh particular symbols. Thus the odds of losing symbols appearing on the payline became disproportionate to their actual frequency on the physical reel. In 1984 Inge Telnaes received a patent for a device titled, "Electronic Gaming Device Utilizing a Random Number Generator for Selecting the Reel Stop Positions." International Gaming Technology IGT bought the Telnaes patent and now all slot manufacturers using what has come to be known as Talneas mapping or reel mapping must license the patent from IGT. The 1984 patent granted on this technology (United States Patent No. 4 448 419) states: “It is important to make a machine that is perceived to present greater chances of payoff than it actually has within the legal limitations that games of chance must operate.

Skill stops
Skill stop buttons predated the Bally electromechanical slot machines of the 1960s and 70s. They appeared on mechanical slot machines manufactured by Mills Novelty Co. as early as the mid 1920s. These machines had modified reel-stop arms, which allowed them to be released from the timing bar, earlier than in a normal play, simply by pressing the buttons on the front of the machine, located between each reel.

'Skill stop' buttons were added to some slot machines by Zacharias Anthony in the early 70s. These enabled the player to stop each reel, allowing a degree of 'skill' so as to satisfy the New Jersey gaming laws of the day which required that players were able to control the game in some way. The original conversion was applied to approximately 50 late model Bally slots and is the first known use of the skill stop on slot machines. Because the typical machine stopped the reels automatically in less than 10 seconds, weights were added to the mechanical timers to prolong the automatic stopping of the reels. By the time the New Jersey Alcoholic Beverages Commission (ABC) had approved the conversion for use in New Jersey arcades the word was out and every other distributor began adding skill stops. The machines were a huge hit on the Jersey Shore and the remaining unconverted Bally machines were destroyed as they had become instantly obsolete.