Slot Machine Information

The History of Slot Machines

It has now been over 100 years since the first slot machine was invented and slots have become one of, if not the most popular casino games. A timeline of the history of slots gives you some idea of how this has happened.

The first slot machine, Liberty Bell is invented by Charles Fey – a mechanical engineer from San Francisco.
The Mills Novelty Company releases the Mills Liberty Bell – a new version of the original game with new symbols.
After the instant popularity of slot machines anti-gambling lobby groups managed to get the games (and all gambling) banned in Nevada.
Slot machines re-appeared camouflaged as vending machines to evade the ban. Gum or candy replaces coins out as is the reason we have fruit symbols on slot to this day.
Gambling is legalized in Nevada with the passing of the “Wide Open Gambling Bill” and slot machines are once again a big hit with players.
The first electro-mechanical slot, “Money Honey” is released by Bally Manufacturing moving from spring mechanisms to electronic parts.
Fortune Coin is released and marks the first use of a video screen on a slot machine introducing a new era in slot machine technology.
The final manufacturing run of mechanical slots by Mills-Jennings Company marking the beginning of the end for mechanical slot machines.
Caesar's Boardwalk Regency opens in Atlantic City with 50% of its slot machines electronic marking the start of a new era in slot technology.
Aristocrat introduces the first 5 reel, all electronic slot – Wild West.
IGT introduces Megabucks, the world’s first wide area linked progressive slot. Megabucks was the first every game to offer the same jackpot at multiple casinos.
The first online casino sites launch and slot machines can now be played by anyone with a computer and Internet connection.

How Slots Work

Although they may look different all modern slot machines work the same way. All slot machines including single pay line, multiple pay line, video slots and slot machines on the Internet share the same basic computer logic.

Please Note - All guides on Slot Players World refer to Vegas style slots which are also known as Class III games. Class II games are based on bingo and a central server.


At the heart of every slot machine is the random number generator (RNG). This part of the game logic does one important task – generate random numbers. The moment you press spin or pull the handle a random number is selected and this maps to the reel positions.

The RNG is constantly generating numbers even when no one is playing.

The Reels and Symbols

Every slot machine has a set of reels and symbol positions that the RNG maps to. For example, each reel has 10 symbol positions counting from 01 to 10, 11 to 20, 21 to 30, 31 to 40 and 41 to 50. An outcome from the RNG could be 0513293350 and this would display the symbols in these positions along the middle line of the game.

The Pay Table

The pay table indicates how much you win from each of the various symbol combinations. Every win combination on the pay table makes up part of the overall theoretical payout percentage.

What Happens When You Press Spin

Each time you start the reels spinning the following steps take place,

  1. A number is selected from the RNG output.
  2. The reels spin and stop at the positions mapped to the RND outcome.
  3. Any line / way or feature wins are calculated based on the symbols displayed.

The outcome of every spin on a modern-day slot machine is decided the moment you start the reels spinning. The spinning of the reels whether it be an animation or physical reels spinning is purely to make slots more entertaining.

Are Slots Random?

Yes, every spin is in no way related to the last spin or the next spin. Every time you set the reels spinning the RNG generates a random number. It is for this reason that it is very possible to hit two big winning combinations in a row, it happens more than you would think.

It is also worth noting that although every spin is random not every combination has the same chance of being hit. The lower wins will be hit many more times than the top prize. This is because there are quite simply more lower paying symbols on the reel than higher paying ones.

Payout Percentages

Every game has a base payout percentage (also referred to as RTP or Return to Player) that is determined by the amount and type of symbols on the reels. By adding more symbol positions or more high or low paying symbols the overall payout percentage can be increased or decreased.

The set payout percentage reflects millions of spins and will not be anywhere close to what you get during an individual gaming session.

On games with some sort of bonus feature or progressive jackpot the final payout percentage calculation also includes any bonus games or jackpots. For example, if you have a Wheel of Fortune style bonus the payout percentage is calculated by adding the payout percentage from the reel layout to the percentage return from the wheel bonus.

All games come configured from the manufacturer at a set level and this cannot be altered by the casino. This is because all game logic is contained within an EPROM chip which once delivered to the casino is a read only memory chip. This theoretical RTP never changes throughout the life of the machine.

Theoretical Vs Current RTP

It’s important to remember that the theoretical RTP for any game relates to the return over millions of spins and never changes. The current RTP from a single machine will vary widely and you as a player will never get exactly the payout percentage a machine is set at. This is a good thing as it would hardly be any fun if you were guaranteed to lose every time you played.

Slot Volatility

All slot machines have a volatility rating. Volatility refers to the frequency and size of wins a machine pays out. Two games could have the same payout percentage, but the playing experience will be totally different due to different volatility. Slot makers typically rate machines, Very High, High, Medium, Low, or Very Low.

High Volatility

The frequency of wins is lower, but the value of wins is higher.

Low Volatility

The frequency of wins is higher, but the value of wins is lower.

In terms of gameplay, you will on average get more spins for your money on lower volatility games compared to higher volatility games.

How to Play Slots

If you’ve never played a slot machine before it is easy to get started. Unlike some other casino games there are no special skills required when it comes to slots.

Step by Step

  1. Select a machine
  2. Insert money
  3. Select bet size and / or lines
  4. Press spin to play

The Buttons

All slot machines have a series of buttons that you press to select different options. Depending on the game format you may or may not have every button option. Common buttons include,

  • Bet per line

    Selects the number of credits to bet on each pay line.
  • Lines

    Selects the number of lines to play
  • Bet Max

    Selects max lines and credits and starts the reels
  • Spin

    Starts the reels spinning
  • Gamble

    After a win this button starts the gamble feature
  • Start Feature

    After winning a bonus this button starts the feature
  • Cash Out

    Press to take out any credits on the machine

Slot Machine Types and Variations

Slots have come a long way since their invention and today there is an almost limitless range of different formats and game types.

Reel Style

There are two main reel categories that slot machines fit into – classic or video slots.

Classic Slots

Also known as Steppers, these games feature physical spinning reels and resemble the original Liberty Bell game. Games most frequently feature three reels and between 1 and 5 pay lines.

Video Slots

Any game that uses a screen instead of actual reels is known as a video slot. Games typically feature five virtual reels and can come in a wide variety of line and ways formats.

Classic Vs Video Slots

At first glance it might seem logical that 3-reel games would offer better odds of winning compared to video slots, but this is not the case. The odds of winning on today’s slots are in most cases comparable.

Games with less reels will tend to have more virtual symbol positions. One major difference between video and classic slots is the volatility.

Lines and Ways

Wins on slot machines are awarded by lining up symbols on lines (or ways) and there are a wide range of different formats.


Slots started with just a single line, but even classic slots quickly progressed to 3 or 5 lines. The introduction of 5 reel slots offered the chance to add more ways to win with additional lines. Common line formats include 5, 9, 20, 25 and 50 lines.

Line wins typically pay with symbols aligned left to right although there are games that pay both ways and games where any symbols on a line pay regardless of left right alignment.

Diagram of the line layout on a 9 line slot machine
An example of the line layout on a 9 line video slot


In 1996 Aristocrat introduced a whole new way of winning with the Reel Power 243 Ways to Win games. Instead of having to line up symbols on lines wins pay based on symbols anywhere on consecutive reels from left to right.

Why 243 ways? If you multiply the number of symbols on each reel you get the number of ways. So 3x3x3x3x3 = 243. The Ways format has been expanded on by increasing the height of the reels. For example, 1024 ways games feature reels with 4 symbols displayed (4x4x4x4x4 = 1024).

Jackpot Types

Jackpot refers to the highest possible pay on a slot machine. All slot machines feature one of two types of jackpots – fixed level or progressive.

Fixed Level Jackpot

The top prize on these games never changes and is indicated on the pay table as a set number. Typically, all games of the same title have the same top jackpot.

Progressive Jackpot

The top prize on progressive games grows from a seed value until it is won and then resets to the seed level. Every bet made on a progressive game adds money to the jackpot value. There are four types of progressive jackpots,

  • Stand Alone

    The jackpot is available on an individual machine only.
  • Linked Bank

    The same jackpot is available on a group of machines.
  • Venue Wide

    The same jackpot is available on multiple machines at one casino.
  • Wide Area

    The same jackpot is available on machines at multiple casinos.

Features and Bonuses

To make slots more exciting, manufacturers started adding bonus features which offer additional ways to win on top of the line and way wins. Some of the most popular features include,

  • Wild Multiplier

    A wild symbol multiplies any win it is a part of.
  • Free Spins

    Free games often with a multiplier for the bonus games.
  • Wheel of Fortune

    A spinning wheel with segment awards a prize.
  • Pick a Win

    Players select items and prizes are awarded.
  • Hold and Spin

    Prizes on the reel are held and re-spins can award extra prizes or jackpots.

Slots Myths

There are many myths relating to slot machines, from warming up coins to avoiding machines that have just paid out. The most crucial point to always remember is that there is absolutely nothing that you can do as a player to affect the outcome.

Myth or Fact?

Myth : All combinations have the same odds

This is where people confuse the fact that slots are random with the assumption that each symbol combination has the same odds of appearing.

Fact : Winning combinations have different odds

This is because there will be more lowing paying symbols or blank positions on the reels compared to high paying ones.

Myth : I should get the listed payout percentage

A player assumes that a machine that is listed with a payout percentage of 97% means if they put in $100, they should get $97 out.

Fact : You will never get the exact payout percentage

Game payout percentages refer to the results over millions of spins. Individual session will vary widely and depend more on game volatility.

Myth : A machine will not payout after a big jackpot

Some players believe that a machine will have a period of no payouts after a big jackpot is hit.

Fact : Every spin is random

Each spin has exactly the same chance of winning and is in no way effected by the spin before or the spin after it. While unlikely it is possible to hit two jackpots on consecutive spins.

Myth : Another player just won MY jackpot

Ever just left a machine and another player has sat down and hit a big jackpot? You may have thought to yourself if only I kept playing that was my jackpot.

Fact : You would not have won

The chances of you hitting the same combination would have been highly unlikely because you would have had to hit the button at exactly the same moment, down to the millisecond.

Myth : If a machine feels hot it means its ready to pay out

Some players think that if you walk around and find a machine with a hot temperature that this indicates that the machine is about to pay out.

Fact : Lightbulbs in the machine make then warm

Machines can feel warm to the touch for no other reason than they have lightbulbs inside them which generate heat. This myth is dying out with the invention of LCD lights.

Myth : Playing straight after someone loses means the machine is due

Many players wait for someone to leave a machine they have lost on and then think that because the player before did not win that they will.

Fact : The odds of winning never change

The odds of winning never change no matter how many people have played a machine or how much money the person before you put into the machine.

Myth : I can tell that a slot is about to payout

A player can determine that a slot machine is going to pay out by walking around and looking at the symbols from the last spin played.

Fact : Every spin is random

The symbols you see on a slot that no one is playing are simply the result of the last spin on the machine. Every spin is random and in no way related to the previous spin.

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