How Do Slot Machines Work?

Slot machines come in various shapes and sizes, and are, by far, the most popular form of casino games not only in Michigan and the rest of the US, but the world. Many also consider slots to be the simplest of all casino games and a perfect way to start your casino adventure.

But how do they work? What lies beneath all those reels, paylines, bonuses, and razzmatazz?

Read on to find out more about the one-armed bandits and the intricate ways in which they operate.

Random number generator software

Among the most frequently asked questions about slot machines is this: How do we know the games are fair? The answer is simple. All slot machines operate via a random number generator, aka RNG.

An RNG is a complex algorithmic system that generates entirely random outcomes of spins. The algorithm ensures that no matter how much time you spend playing a game, or how much money you’ve wagered, your odds of winning are the same with each spin.

The RNG system is among the most important aspects of every slot game, and all gambling jurisdictions that license software providers pay special attention to game mechanics to ensure all is safe, secure, and fair.

Reels and paylines

All slot games are characterized by the existence of the reels and paylines that the game’s symbols use to make winning combinations. Slot games can be divided into categories depending on how many reels and paylines they feature.

Classic slots are ones with three reels and anything from a single payline to five paylines, while video slots are games with five or more reels and a large number of paylines.

Slot reels are filled with symbols that land at random as a result of each spin. The paylines are imaginary lines across the reels that form a playing grid. Usually, three or more identical symbols are necessary to make a winning combination on a single payline.

To initiate a spin, a player hits the spin button and sends the reels into motion. If three or more identical symbols appear on a payline, then the player gets a corresponding payout or triggers the game’s bonus feature, depending on the type of the symbol and the gameplay.

Nowadays, the game engines are so complex that the reels don’t necessarily have to spin to provide the symbols, and the symbols can fall into different places on the reels, form clusters instead of winning combinations on lines and plenty of other mechanics.

Weighting of slots

There is an intriguing part of slot machines that has to do with the reels and the hit frequency of some symbols in the game. This phenomenon is called weighted reels, and it has more to do with land-based slots than the virtual ones.

First, the number of symbols on a physical reel is limited by the circumference of the actual reel, so software designers created a virtual reel housed inside a computer chip in the slot machine. These virtual reels determine the stopping position of the physical reel and whether the reel will stop at a blank spot or one with a paying symbol. The virtual reel has all the same blank and symbol position as the physical reel, but spread across many more positions so that a symbol from the actual game can be found on multiple positions on the virtual reel.

When the RNG algorithm comes up with a number, it will correspond to a position on the virtual reel, and that is the one the physical reel will stop on. This allows the software providers to determine the hit frequency at all times and determine how much the slot will pay, whether the reel will land on a higher- or lower-paying symbol more often, etc.

This complex mathematical work can also affect the players’ judgment when it comes to winning. Namely, you will frequently find that when two paying symbols are on a payline, the third missing one is just above the blank space. This creates the illusion of a near win. A number of papers have examined this topic and how it affects the gambling behavior of players.

Just because a slot gives the impression that it could hit, doesn’t mean it will hit.


No matter the type of video slot you want to play in either an online or land-based casino, all of the games will have specific symbols. The symbols in games are designed to match the theme of the slot, and they can range from fruits, bells and numbers in classic slots to more elaborate and detailed symbols, including some with animations.

Typically, the symbols in a slot game have different values. There are lower- and higher-paying symbols, with the lower-paying ones often appearing as card symbols that range from 9 to ace and the higher-paying ones appearing as characters that reflect the theme of the slot.

However, the most valuable symbols are the wild and scatter symbols that trigger the slot’s bonus features or can be used as a substitute for other basic symbols in a winning combination.

Bonus features

The majority of modern slots come equipped with a series of bonus features that players can trigger by landing particular scatter or bonus symbols on the reels. The bonus games that get activated bring lucrative payouts and can lead the players into mini bonus games with a different set of reels and paylines.

The most common forms of bonuses in slots are free spins bonuses where players get a number of free spins that have the same value as the real money bet that activated the bonus in the first place. Take IGT’s classic slot game Da Vinci Diamonds, for example. When three bonus symbols land on a payline and the first three reels, players will automatically receive six free spins. If during these free spins three or more bonus symbols appear, that leads to additional free spins, so in total, players can be looking at 300 free spins.

Also, there can be several prize multipliers in those bonus rounds that can multiply the winnings by 100x or more.

Payouts — RTP and house edge

Winning is what all Michigan’s online casino players are after, and slot games can offer some impressive payouts. The win rate on a slot game is set by the return-to-player ratio or RTP. The RTP is actually a calculation of how much a video slot game is expected to pay back after a period of time, expressed in percentages.

For example, a slot game with a 95% RTP is expected to pay back 95¢ for every $1 wagered. However, note that this ratio does not represent the short-term likelihood of your winning, but is in fact measured on a long-term basis, over the lifetime of a slot machine. In the case of online slots, this could be hundreds of thousands of spins, or more.

The RTP does not guarantee a large win, either. Wins could be very small, as long as they end up paying out the percentage stipulated on the machine.

Every slot game is special and distinct, but there are aspects all games share, such as reels, paylines, bonus features, and RTPs. The most important thing to remember is to have fun while playing and gamble responsibly.

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