The basic design includes three reels mounted on a central shaft.

There are any number of ways to arrange these elements, and manufacturers have tried dozens of approaches over the years, so we'll focus on one representative design. A coin detector initially registers that a coin has been inserted and unlocks a brake so the handle can move. A braking system brings the spinning reels to a stop, and sensors communicate the position of the reels to the payout system. This shaft is connected to a handle mechanism that gets things moving. The central element is a metal shaft, which supports the reels. The classic slot machine design works on an elaborate configuration of gears and levers. We'll also see what determines the odds of winning on a slot machine and look at some popular variations on the traditional game. In this article, we'll find out what sets the reels in motion in modern slot machines as well as in the old mechanical models.

The amount you win - the payout - depends on which pictures land along the pay line. If each reel shows the same winning picture along the pay line, you win (certain single images are sometimes winners as well). Winning or losing is determined by which pictures line up with the pay line, a line in the middle of a viewing window. The player pulls a handle to rotate a series of reels (typically three) that have pictures printed on them. The classic mechanical designs have been almost completely replaced by computer-controlled machines. The technology of slot machines has also changed a lot over the years.

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