These slots are essentially the same, but for one feature: flat tops will pay the winner a predetermined amount, whereas progressive slots have a jackpot that grows by a percentage of each coin played. Oftentimes a number of progressive machines feed into one jackpot where any machine in the group can win, and the jackpot grows into an astronomical amount. These groupings can be a number of machines in one casino, or can be tied to all of the same machines in a whole state. Progressive machines can be identified by flashing electronic payoff signs displayed either on top of the machine or above a grouping.

There are many different types of machines, and whether playing a progressive or a straight slot, players will be faced with a number of choices. Machines vary on denomination of coins, the number of reels, how many coins to play, and single or multiple pay lines.

The most common machines have 3 reels, but casinos do offer machines with 4 or 5. When it comes to the odds of winning what is most important are the number of reels a machine has, and how many symbols are displayed on each reel. Essentially, the greater the number of reels and symbols, the harder it is to hit the jackpot or any other winning combination. The number of symbols on each reel is programmed into the computer that operates the slot machine, and the actual number of symbols depends on the size of the jackpot that the machine offers. The reason for the programmed symbols is to make the jackpot rare enough that the machine will generate enough money to pay for the jackpot and yield a profit for the casino.

Most machines are set to pay out anywhere from 83 to 98 % of the coins that are played in the course of a pay cycle. On average, machines operate on a 2 or 3 coin maximum. When it comes to multiple coin playing machines, there are subtle variations. With some machines, the number of coins played is proportional to the payoff, and with others, the payoff is more than proportional. Some machines don't even pay a jackpot on 1 coin, and the 3-coin jackpot often pays 150 % of a 2-coin win. In this case it is best to play the maximum number of coins.

The standard slot machine has one pay line, but 3 pay lines are not that uncommon. For multi-lined pay lines, a coin must be played for a specific pay line in order for that pay line to be eligible for a win. When players hit one of the smaller winning combination they will be paid automatically by the machine. The larger jackpots however, will be paid out directly by a casino employee who is notified by a light on the top of the machine. Each casino's slot payoffs will vary.