How Slot Machines Work

Most people have seen a slot machine before, and most people have a general idea of how such a game works. You put money in a machine, pull a lever, watch the reels spin, and if the symbols land in a certain way, you win money. Those are the basics, and most people understand that much.

This page goes into a little bit more detail about the innards of the machine. Traditional slot machines were all mechanical, while modern slot machines are mostly computerized video games, even if they don’t look like it. How they stay profitable and how they keep millions of gamblers practically addicted are the most interesting questions we try to answer.

The Components of a Slot Machine

A slot machine has a lot of working parts, and all of them are important. We’ll look at each of those parts below:

Reels – The things that spin on the game are called the reels. These used to be actual metal hoops that were actually quite large, but on modern games, these reels are virtual. Many slot machines have three reels, but five reel slot machines are becoming increasingly popular.

Symbols – If the reels were blank, then slots would be a dull game. Instead, the reels feature multiple themed symbols that help the player understand whether or not she’s won on any given spin.

Paylines – Most folks understand that if they line up three of the same symbol in the center of the screen, then they’ve won something. On modern games, sometimes as many as 25 different paylines are available. Slot machines with five reels often feature large numbers of paylines, too.

The Pay TableThe pay table shows which combinations of symbols result in which payouts. For example, three cherries in a row might pay out $100.

Play Buttons – It’s not as simple as just putting a coin in the machine. You have to decide how much to play. The play buttons are how you decide how many lines you’re going to wager on, and they also determine how much money you’re going to bet on each line.

The Random Number Generator – This is a computer program inside the machine which determines the outcome of each spin. It’s often abbreviated as RNG.

How It All Comes Together and Works

Early slot machines were entirely mechanical. Each symbol on each reel had an equal chance of coming up, so the limited number of reels and symbols limited the size of the jackpots. Having more than ten or twenty symbols on each reel would make the machine too large to be practical.

Modern slot machines are computerized, and even though they might look like traditional slot machines, the way they work on the inside are considerably different.

Modern slots use a random number generator to come up with an outcome for each reel. Since it’s a computer, it’s not limited to providing an equal chance of each symbol coming up. Some of the symbols can come up more often or less often.

Also, reels are no longer limited in the number of symbols available. Since these reels are imaginary, they could have an almost infinite number of symbols available, although practical games usually limit themselves to 50 or fewer.

Weighted Slots

When people discuss “weighted slots”, they’re talking about the likelihood of each symbol coming up on a modern slots game. For example, if a particular symbol is programmed (or weighted) to only come up with a likelihood of 1/56, then getting three matches of that symbol only happens once in every 175,616 or so. That allows the casino to offer a huge payout, since that’s going to happen so rarely.

The other symbols might be weighted to come up more often. For example, another symbol might be programmed to come up once every 28 spins, while another might come up as often as once every 7 spins. The payouts for matches on those symbols will be correspondingly smaller.

How Does the Casino Make Money from Such a Machine?

Casino games all make profits because they pay out prizes that are smaller than the odds of hitting them. Slot machines are casino games, so they work the same way.

A simple slot machine game might have three reels and five symbols. The chances of getting a jackpot would be 1/5 X 1/5 X 1/5, or 1/125. If the slot machine is programmed to pay out 100 to 1, then it’s easy to see how the casino would make a profit in that situation.

Of course, the payouts on slots are more complicated than that, but the math has been done, and the manufacturer and the casino know within a hundredth of a percentage point how much money they expect to make per spin.

The gambling industry calls this number the payback percentage. It represents, on average, over tens of thousands of spins, how much money is paid out as compared to how much money is paid in on a gambling machine. For example, if a game has a 90% payback percentage, and you’re playing $1 per spin, you can expect to win, on average, 90 cents per spin over the long run.

Of course, in the short term, anything can happen, which is why people still play slots. If there were no chance of winning, players wouldn’t play, and the casinos would make no money from such a device.