Originally, casinos installed slot machines as a diversion for casual gamers. Unlike traditional table games, such as blackjack or craps, slot machines don't require any gambling knowledge, and anyone can get in the game with a very small bet.
This idea proved to be a monstrous success, slot machines eventually moved off the sidelines to become the most popular and the most profitable game in town, bringing in more than 60 percent of the annual gaming profits in the United States.
The classic mechanical designs have been almost completely replaced by computer-controlled machines. But the game has remained the same. The player pulls a handle to rotate a series of reels that have pictures printed on them. If each reel shows the same winning picture along the pay line, you win and sometimes certain single images are winners as well. The amount you win depends on which pictures land along the pay line.