A slot is a narrow notch, groove or opening, as in a machine for accepting coins or in a door for a lock. It may also refer to a place or time reserved for an activity, such as the time slot for a flight or appointment.
The first mechanical slot machine, invented by Charles Fey, had three spinning reels with symbols that lined up to make poker hands when a lever was pulled. It was wildly popular and led to the proliferation of similar machines in saloons and gambling halls across America. By the 1920s, morality and law began to restrict their operation. By 1951, most of them were outlawed except in Nevada and private social clubs.
In modern slots, a random number generator (RNG) determines the results of each spin, without the visible reels. Instead, microprocessors inside the machine assign a weight to each stop on multiple reels, so that a particular symbol appears more often on a given reel than it would if there were no computer control. The weighting of symbols can be adjusted to give different payouts or jackpot sizes.
Game designers are constantly watching the habits of players and learning from the results of their games. “Persistent play is an indicator of what keeps players engaged,” says Konami’s Arrowsmith. Research also includes hands-on experience with the actual game, which allows designers to get a feel for what features are most effective. “This is something that we’re continually looking at,” adds Scientific Games’ Mastropietro.