The first mechanical slot machines were introduced in the 1890s and typically rewarded winners with token prizes like cigars or sweets. Players inserted a penny in the slot and pulled on a lever to start the reels spinning; if the proper symbols lined up in the proper order, the player won. These first machines used springs to release and spin the reels and a notched braking plate to stop them. The first electric slot machines were developed in the 1930s and used a motor to activate the reels. Players pushed a button instead of pulling a lever, but the basic principle remained the same: the player won only if the symbols on the reels lined up in the proper order. It wasn't until the 1960s that electromechanical technology allowed for significant variations in both games and payout rates.

Today's slot machines, though they may resemble their mechanical ancestors right down to the lever, are controlled by computers and microprocessors. Computer technology has promoted a greater variety of games and truly stunning visual and audio components, making slots more enticing and exciting to play. Computers also allow casinos to be far more precise in regulating machine payouts and tracking player activity.