How Do Slot Machines Work? Secret Mechanics of Land-Based Slots

How Do Slot Machines Work? Secret Mechanics of Land-Based Slots

Slot machines are an extremely popular form of gambling. The premise is simple: you insert a coin, pull a lever, and reap in cash rewards if the symbols on the reels align in a certain way. Slot machines test your luck and intuition, and, despite the simple rules, they are not boring in the slightest.

Slot machines use catchy music, fun graphics, and interesting symbols to hold the player’s attention. But how slot machines work? What are they made of and how do they determine when to pay out and when to disappoint the not-so-lucky players? 

This article uses advanced terminology. If you are new to slots, you may want to check out our complete glossary of slot game features.

The Anatomy of a Slot Machine

So how do slots work? In order to find that out, you’ll need to go through video slot parts. When playing a land-based slot machine, you will see the following components:

Coin Slot/Bill Slot

This is where you put your money into the machine. You can also insert a cashed-out ticket into a slot machine and spend your winnings on additional spins. 


Slot machines usually feature three or five reels, but you can occasionally come across machines with as many as ten reels! Reels are the spinning mechanisms that make the vertical positions on a slot grid rotate. Each reel has a certain number of “steps” where it could stop, and each step either contains a symbol or is blank. A typical slot machine contains about 20 stops on each reel, but this can vary.

Slot machine insides that show how slot machines work.


In older slot machines, the lever would actually set the reels in motion. In modern slot machines, however, the lever just triggers the casino game’s software, which, in turn, makes the reels spin. 

Play buttons

Slot machines may feature several different buttons. The most common include “Spin Reels”, “Play One Credit”, “Play Two Credits”, “Bet Max Credits”, “Cash Out”, and “Request Change.”

Coin Tray

In the past, once you would hit the “Cash Out” button, your coins would cascade out of the machine and pool in the coin tray. Now, however, it is now more common for the machine to print you a cashout voucher. These are redeemable at a redemption machine or at the cashier’s cage. Alternatively, you can insert it into another slot machine (usually through the bill slot) and go for some more spins. 

Coin Tray of a slot machine, one of the most essential components.


The payline is the horizontal line that you can see in the center of a slot machine’s screen. In order to land a winning combination, the symbols must align on an active payline. The number of paylines available can vary from game to game, but you can only win payouts on the paylines that you place a bet on.

If there are ten paylines available, and you only bet on two of them, you can only reap those two payline’s rewards. Some machines require users to pay one credit for each payline that they would like to activate. Other machines may require multiple coins to activate a single payline. 

Some slot games allow players to adjust the payline’s direction, while others are fixed. Paylines can run left-to-right or take on a zig-zag shape. 

If you’re also interested in how all of these parts come together, make sure to watch this How It’s Made feature on casino slot machines:

Pay Table

A slot machine’s pay table will display all of the game’s winning combos and corresponding payouts. It will also display any special bonus, wild, or scatter symbols. Furthermore, the pay table will show the game’s current jackpot and indicate whether or not the machine is progressive. You should always check out a slot game’s pay table to educate yourself on all possible wins, payline configurations, payout odds, and information for bonus events. 


Every slot machine will clearly display the basic information relevant to its users. Some common displays include:

  • Credits played. This display shows the exact number of credits that the player is betting on each spin. 
  • Credits. This will show the player how many remaining credits they have. When the display reaches 0, the player must deposit additional coins through the coin slot in order to keep playing. Keep in mind. each credit will align with the denomination the game requires. If a player is using a 25-cent machine and inserts a $10 bill, the display will show that the player has 40 credits available. 
  • Insert Coin. This display shows that the slot machine is not currently activated. Anybody simply has to insert bills or coins into the machine to begin playing. 
  • Winner Paid. This will show how many credits were won on the previous spin, which would be added to the player’s total on the Credits display. 
  • Error Code. This display will only activate if a slot machine is malfunctioning. It will show a code that assists a staff member in identifying the problem. 

Feel free to also watch a video guide on how a casino slot machine works below:

Types of Slot Machines

There are many different kinds of slot machines, some of which can be difficult to find. Here are some types of slots that you might come across and a short guide on how they operate. 

Single-Coin Machines

These used to be very popular but are now much harder to find since most slots now accept dollar bills or require multiple coins per spin. Because these machines only accept one coin per spin, the house does not rake in as much revenue during a period of time as it would when using a multi-coin machine.

However, some old-fashioned casinos still use these types of machines. If you want a more classic gaming experience, and you want your credits to last for more spins, try out a single-coin machine. 


Not to be confused with Multiplier symbols, a multiplier machine takes multiple coins and has a payout ratio that corresponds with the number of coins that a player uses on a spin. This type of machine was introduced in 1987 and is now the most popular type of slot machine found in modern casinos. 

Multiplier machines still allow players to partake in single-coin play, but often players will choose to make the maximum bet. 

Buy-Your-Pay Machines

Buy-Your-Pay machines allow players to bet between 1-5 coins on each spin. The number of coins inserted is what determines the game’s number of activated winning combos. For instance, if a player inserts only one coin, 3 “bars” would be a winning combo, but not 3 cherries. On the other hand, if they insert more coins, then both combos would be considered winning ones. 

You can identify this type of machine by taking a look at the pay table. If it shows that more coins unlock extra winning combos, then you know it is a Buy-Your-Pay machine.

This kind of machine is not as common as multiplier machines. Many players avoid using them because it can be frustrating when they are just one coin shy of cashing out a great combo.  

Multiple Payline Machines

Paylines in a slot, the most important factor of how a slot machine works.

Most slot machines only have one payline, which is in the middle of the game’s screen. On the other hand, a multiple payline machine has more than one active payline, as its name implies. This gives players a more exciting experience and offers more win potential.

However, players will typically need to pay an additional credit to activate each payline. When a payline is activated, it will light up. 

Land-based casinos’ multiple payline machines typically offer 2-5 paylines, but sometimes more. On the other hand, online machines could have 50+ paylines! 

Progressive Machines

Progressive machines are linked together by one jackpot, which can grow to gigantic proportions since it grows anytime a player inserts a coin into one of the network’s machines. When a player finally hits the jackpot symbol combination, the pool will reset. Some US gambling venues have linked together slot machines across entire states! Over the years, this type of slot machine has become very popular, since everybody wants to try their hand at winning a jackpot that would make them a millionaire. 

Progressive jackpot slots have become especially popular in online casinos, and slots across various websites can be linked, as long as they use the same software platform. 

Big Berthas

A Big Bertha slot machine simply refers to a machine that is gigantic and features 3+ reels. Some even feature as many as 8 reels, and each reel has 20 symbols! These machines are typically located near the entrance of a casino, to draw in attention. However, they don’t offer a great payout percentage.

Woman pushing lever of a giant slot machine nicknamed Big Bertha.

Multi-Game Machines

A multi-game slot machine allows the player to switch between various games without having to sit at a different machine. For example, one multi-game machine might offer slots, blackjack, and video poker. In addition to this, multi-game machines will usually support many different currency denominations. 

Other Useful Terms to Know

Hit Frequency

Hit frequency refers to how often a winning combination will land on the reels. If a machine has a high hit frequency, this means that winning combos will land more often. Machines that hit often don’t have a great payback percentage. Conversely, slot machines that have a low hit frequency will usually have a pretty significant payout rate.

Payback Rate

The payback rate, also known as payback percentage, refers to the amount of money that gamblers win, compared to how much they wager. Slot machines’ payback rates typically fall between 82% to 98%. 


Each slot machine has a built-in Random Number Generator (RNG), which is an algorithm that ensures that each landing symbol is totally random and is not dependent on a player’s previous spin. 

Now that you know all the details about slot machines, come try out some virtual ones at CasinoChan!