Being one of the most popular casino games in not just Canada – but the world – slots are loved by many a gambler. Whilst modern slot machines and video slot machines work on the same principle as they did when slots were first created back in 1899, many still wonder how are slots machines programmed exactly?

In this blog post we’re going to go in depth with the question “how are slot machines programmed?”, telling you all about what every smart slots player should know: whether slots really are random; what are the probabilities of winning and the RTP; how the casino actually makes money; common myths about slots and even more.

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How Slots Actually Work

When you visit an online casino and click to play on most of the slot machines, you’ll see the games still use the age old system of reels to show the result of every spin you make. Even though you see the reels, they’re just the visual component to the maths that are being worked out.

The great thing about these modern online slot machines and video slots that you find at online casinos is that they can have crazy bonus rounds and features that weren’t possible with early slot machines. The mechanical reels of the old slots wouldn’t be able to handle the bonus rounds such as numerous free spins, scatters, expanding wilds and more.

Are Slots Really Random? – The Random Number Generator

The main thing that makes all slot machines work is the random number generator (or RNG). The outcome of every single round when you play on a slot machine is dictated by this random number generator. The number that is generated by this random number generator will “speak” to the machine and tell the reels of the machine exactly when to stop, deciding what the result of the spin is.

The flow of the system goes something a little like this:

  1. The RNG system of the slot machine generates a totally random number.
  2. The mathematical part of the slot machine works out the randomly generated number and works out where each reel should stop.
  3. The game will then work out the outcome of that spin depending on where the reels have stopped – whether you win something or not.
  4. The outcome is then showed to the player.

Every spin you make on a slot machine will come down to pure luck. Each outcome of the slot machine is totally independent and not affected by any previous result of yours or any other players, just like roulette. It’s just you and pure luck.

Modern RNG systems that are used on online slots are actually hardware devices that are built to generate a random number from something called electro magnetic noise. The best way to picture this is like an old TV set that doesn’t have a signal – just a scramble of little black and white dots. Each black pixel is counted as a ‘1’ and each white pixel is counted as a ‘0’. You would then take a picture of one part of the scrambled TV screen, convert each black and white pixel into the corresponding ‘1’ or ‘0’ and then write the number into a text file. There’s your random number!

The special hardware that online casinos use in their slot machines can generate thousands of these random numbers every single second. Because of this, every single time you press the play button, a different random number will be generated, meaning the outcome of the spin will always be fair and random.

How the Casinos Make Money

So if the slot machines aren’t rigged in any way, then how do casinos actually make money on them? The simple answer is that the humble slot machine is designed so that it will always pay out less over the long run, ensuring the casino always wins in the end.

An example of this would be playing a simple game of heads or tails. You give me $10 to start off, and if it comes up heads, I’ll give you $15 back. If it comes up tails, you lose. In the long term, the advantage will always be on my side because of the maths. You can play just a few rounds and maybe end up with a profit, but over the long run the game always runs in my favour.

Slots are very similar but with a more complicated system. There’s a bit more math involved with the online slots, including factors such as: matching symbols on virtual reels; the different sized wins on the paytable; any progressive jackpots; the different probabilities and rules of the bonus rounds and features; and the settings of these bonus features.

All in all, this math and the totally random numbers that are generated always end up giving the casino an advantage – even if it’s small – over the player, meaning the online casinos always make money in the long run. This is known as the house edge.

How Slot Machines Are Programmed

Now that we know how the online slots work and the RNG component that decides each and every result, we can take a closer look at how slot machines are programmed.

Because of the vast range of different types of slots that people like to play – like three-reel slots, ones with five-reels, different themes and features etc, different software providers will specialise in producing different styles of casino games and slots. These independent companies offer their games to different casinos, so you can find the same slot on different online casinos.

The process of playing a slot machine on an online casino goes like this:

  1. You initiate your gaming session on an online casino.
  2. Your browser will then communicate with the game servers of the provider of the game – not the actual casino you’re playing on.
  3. The round outcome – including the maths that are involved and the random numbers – are generated by the independent software company; not the casino.
  4. All the casino does is confirm your bet and then notify you about if you manage to land a winning combination or a bonus such as free spins. They get this information from the provider of the slot game.

This means that if you’re having a losing streak, it’s down to pure luck and has nothing to do with the online casino you’re playing on. Even if you end up playing your favourite online slot at an online casino you’ve never played at before, the outcome from the game isn’t down to that casino but the game provider.

The whole process of how the programming of any online slot machine works is like this:

  1. You press the spin button on an online slot game in your browser.
  2. The game then sends a message of ‘spin’ to the game server of the software provider.
  3. The server on the game provider’s side will then calculate what your bet was. This server will ask the casino you’re playing at to take this amount away from your account.
  4. The casino’s server confirms this.
  5. The game provider’s server will then send a request for a random number to be generated.
  6. The RNG will then provide a random number that’s fair.
  7. The server of the game provider will then use this random number to spin the reels of the game and calculate the results.
  8. If it’s a win, then the server on the game provider’s side will ask the casino’s servers to add whatever the winnings are to your account.
  9. The casino servers will then confirm this.
  10. The result is then fired to the game being played in your browser.
  11. Finally, the outcome of the result is displayed, animated and showed to you!

Whilst this sounds like a process that would take a long time, the whole thing is done in less than a fifth of a second.

What are the Probabilities of Winning and the RTP?

The RTP (or return to player) is the average return or payback percentage to any player over the long term of playing that particular slot. In mathematical terms, this payback percentage basically means the total money that has been won on that particular slot game divided by all of the stakes put on the game. These long term statistics are calculated over millions of spins, with the smaller percentage deemed the house edge or casino advantage.

If you play like most other slots players and play a fraction of this amount – so a few hundred rounds – then the return to player percentage can vary wildly, from as low as 30% RTP to a huge 100% RTP if you’re extremely lucky. Working on this logic though, it turns out that the more games you play on any one slot machine the closer you’re going to get to the statistical RTP of that machine.

The most common RTP you’ll find at slot machines is 96%, but some slot games go all the way up to 98.7%. The great thing about RTP is that it’s a number that can be used to compare different slots in terms of potential returns, and it makes it easier for online casinos to advertise these slots as they can declare the RTP of a game.


A more complicated concept than RTP, but one that’s good to know if you want to know more about the programming of slots and how to get the most out of any online slot you play on.

In layman’s terms, higher volatility slots will have higher wins less frequently, whilst lower volatility slots will have smaller wins more often. So depending on your play style, you may want more smaller wins, winning enough to keep you chugging along for a nice gaming session. Or you may want to win the big dollars less often and go for the higher volatility slot games.

The volatility of any online slot can’t be simply stated in a single number like the RTP can. Because of this, game providers and software companies will show the volatility as either low, medium or high. Whilst these categories are much broader to compare than a pin-point number, they give you some sort of idea as to the level of volatility you will experience playing a game.

What to do if you think the slot is rigged

Whilst it’s incredibly unlikely, on the rare occasion, a slot machine may malfunction in some way. Something can go wrong with one of the servers or in rendering the game result. If this happens, you’re best bet would be to take a screenshot of what’s happened and then contact the customer support of whichever online casino you’re playing on.

They will contact the game provider and also have a log of every spin, which will help the casino and game provider analyze whether there was a bug in the game.

Another step you can take is to play games form providers that have the eCOGRA seal of approval. This is an independent company that checks and validates the fairness and randomness of the random number generators of online casino games.

Common Myths About Slot Machines

There are some common myths about slot machines that get passed around between gamblers. Here are some of the most common and why they simply aren’t true:

Myth 1: Slots have different cycles of winning reel combinations. You can work out when a winning combination will land next by figuring out these combinations.

This is a big urban legend in the community and totally false – any online slot machine at a respectable online casino in Canada will be using a random number generator. The whole advantage of the casino – the edge that the house has – is because of how the mathematics of the different systems work out, therefore there’s no need for the online slots to have any type of winning cycles as this would just complicate things.

The simple reality of this myth is that the machine you’re playing on will have streaks of losing spins and streaks of winning spins. These are just because of the randomness of the results, not any sort of sequence or cycle.

Myth 2: Slot machines are programmed in a way so that they won’t pay out after a big win and they’ll pay more when they’ve been filled with money.

This myth stems from players of land based slot machines and the days of the standalone slot machine you find in places like Las Vegas. This is totally false for modern day slot machines though, as machines aren’t standalone any more, with multiple machines connected to one single central server. Many land based casinos also don’t have a direct payout mechanism in the slot machines, with you having to get paid out from the staff, which makes this myth impossible!

Myth 3: Certain buttons or levers on a machine payout less than other ones – such as the auto play or the lever on a one armed bandit.

You know this can’t be true when you realise that the game is all based around maths and the random number generators inside the hardware – and not which button is pressed or not pressed. This is especially relevant with online slots, where the random numbers are not affected regardless as to whether you press certain buttons or use an autoplay feature.

History of the Slot Machine

The very first slot machine was created in 1887, a five drum machine with playing cards on the reels, developed by Sittman & Pitt. The machine was a hit and spawned the next development in slots – the famous Liberty Bell machine in 1899. This three-reel slot quickly became one of the most popular games around with its automatic payouts on winning combinations.

The next big development was in 1907 with the first ever fruit machine – The Operator Bell by Herbert Mills. Then in 1964, the first ever electro-mechanical slot came out, and shortly after, in 1967, the first ever video slot with video reels appeared.

This paved the way for the online slots you see today, with random number generators taking over from tumblers and mechanical-style reels. Most modern slots have unique winning symbols, a big jackpot with progressive style wins and plenty of free spins, a bonus event round and plenty of choice between three-reels or five-reels.

Slot Machine Variants

Thanks to developments in technology and graphics, there’s a huge range of slot machines you can play on, from three-reel slots with graphics that pop out, to video slots with different themes, to slots with multiple free spin bonus rounds.

You’ve also got video poker-style games, which combine the elements of skill-based gameplay that you find in casino table games with the RNG element found in online slots.

Slots FAQs

When do slots pay out?

Due to the randomness of the numbers that are generated, there’s no way to work out exactly when a slot machine will pay out. You may increase your chances of winning on Slots with free spins and bonus rounds, but the game is down to pure luck!

Are slots programmed to be rigged?

If you’re concerned about slot games being rigged on an online casino in Canada, then your best bet is to make sure the casino is fully licensed and has games from providers who have the eCOGRA seal of approval. Both of these things ensure you’re playing on a randomly fair slot game.

Is there a way to beat the house edge?

On most slots, there is no way to consistently beat the house edge and have consistent wins – it’s all down to the RNG.