If you walk into just about any casino the game that dominates most of the floor space is Slots. There is a good reason for this: Slots make up about 60–65% of a casino’s total revenue. Billions of dollars flow through these machines each year. Because of their popularity, slot machines come in a wide variety of denominations and a wide variety of styles.

The original Slot Machine, the “Liberty Bell”, was built by Charles Fey in San Francisco at the end of the 19th century. It’s been a little more than 100 years and now Slots come in hundreds of variations and many are run by a computer board with the output displayed on a video screen.

All Slot machines are not created equally. Lower denomination machines usually have a lower payout percentage. It costs just as much to buy and maintain a $.05 Slot Machine as it does to buy and maintain a $0.25 Slot Machine. Casinos usually adjust for this by having a lower percentage payout for the $.05 Slot Machine. Regulatory bodies set the minimum percentage payback for Slot Machines. The current minimum in Nevada is 75% and the current minimum in Atlantic City is 83%. Because of competition, most slots have a much higher payback.

Source: WorktheOdds.com