Functioning of slot machine
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The functioning of slot machines – An overview

Slot machines are the most popular games in any casino, be it land-based or online, but a lot of people do not have a clear understanding of how they work. Originally, casinos had introduced these as a treat for casual gamers. Unlike conventional table slot machines, there was no need for any gaming experience, and anyone could get a very small bet in the slot games. This idea proved to be a huge success and slot machines eventually moved off the sidelines to become the most popular and profitable game among all.

The slot machine’s invention

We have to go back to when the first slot machine was invented to realise how today’s casino slots operate. Slot machines can be dated back to the late 1800s, when a card-driven mechanism consisting of five reels was invented by a company (Pittman and Sitt) based in Brooklyn, NY.

The functioning of slot machines - An overview
  • From cards to symbols

A San Francisco man named Charles Augustus Fey used a similar idea, only a few years later, to invent a three-reel slot game that used image symbols associated with slot machines.

  • From analogue devices to digital video slots

The 1970s saw the video slot coming to life and were the predecessor to all the digital slot options that today are open to online and offline players. This video slot technology has now moved to the internet, where gamers have been able to play all their favourite slot games without having to go to a particular venue or even leaving their homes. Technology became advanced enough for the first online casinos to spring up in the mid-90s, around the time when everything from shopping to news consumption began moving to the internet. This in turn led to the follow-up of online slots.

  • From desktops to mobile applications

Slots then evolved again, to provide accessibility on mobile devices this time. Thanks to the huge upward trend in terms of mobile device capabilities, mobile slots became available in the 2010s, pioneered by the capabilities of iPhone and Android smartphones and the software developers who produced slot games designed for those devices.

Today, if an online casino does not have a functional smartphone app or a mobile platform with games available for all forms of mobile devices that allow players to play their games anywhere they are, the site might as well be a thing of the past.

The transformation in the technology used:

The technology of these machines has also changed a lot over the years. The classic mechanical designs were almost entirely replaced by computer-controlled devices. But the game is the same. The player pulls the handle to rotate a series of reels (usually three) with pictures on them. Winning or losing is decided by which images line up with the payline, a line in the middle of the display window. If-reel displays the same winning picture along the pay line, you win (some single images are often winners as well). 

The functioning of slot machines - An overview

The amount you receive, the “payout,” depends on which images land in the pay line. These were originally mechanical devices that relied on springs and gears to spin the reels. Modern machines use a computer program called a random number generator (RNG) to determine which symbols land where. A Random Number Generator (RNG) is a computer program that cycles through thousands of numbers per second. When you hit the spin button, the program stops wherever it’s at. These numbers correspond to stops and symbols on the reels.

Here we will find out what sets the reels in motion in modern slot machines as well as in the old mechanical models. We will also see what determines the odds of winning on a slot machine and look at some popular variations on the traditional game. And once you have an idea about the working of the game you can play different variations of the game at trustworthy online casinos like Winissimo. So let us begin without any further delay.

Online vs land-based slots

Online slot machines work just like their land-based counterparts. All the action is handled virtually. But the random number generators work the same. Online slots offer 2 distinct advantages over their land-based counterparts, too:

  • Free play options

  • Higher payback percentages

The basics

The classic design of the slot machine is based on an intricate system of gears and levers. The central element is a metal shaft that supports the reels. This shaft is connected to a handle mechanism that makes things move. The braking system stops the spinning reels, and the sensors communicate the position of the reels to the payout system. The coin detector initially detects that the coin has been inserted and unlocks the brake so that the handle can move. 

The functioning of slot machines - An overview

There are several ways to organize these components, and over the years, designers have tried out hundreds of solutions, so we’re going to focus on one representative style. The basic design consists of three reels mounted on a central shaft. The central shaft also supports three notched discs which are linked to the three reels. A second shaft under the main shaft supports a kicker, a piece of metal consisting of three paddles. The kicker paddles are lined up so that they can push against the notches on the 3 discs. The second shaft also supports a series of attached stoppers, teeth that secure the notches on the discs.

The kicker and the stoppers are both connected to springs, which hold them in a standby position. The kicker is held in place behind the discs, while the stoppers are held up against the discs, locking them into place. When you pull the handle on a slot machine, these parts do a lot of work. Let us explore more.

Pulling the handle

A series of events take place after a person pulls the handle on a slot machine. Here’s a rundown:

  • The handle rotates a hook mechanism, which grabs hold of the kicker, pulling it forward (toward the player).

  • A catch on the opposite end of the kicker grabs a control cam piece and pivots it forward. This rotates a series of gears connected to the control cam. A spring pulls the control cam back to its original position, but the gear assembly slows it down considerably and the gears act as a mechanical delay.

  • When the control cam is pivoted forward, it releases a spring-mounted cam plate extending across the back of the machine.

  • The control cam also pulls the stoppers away from the notched discs. As the kicker keeps moving, it pushes the stoppers against several catches on the cam plate. These hold the stoppers in place, so the discs and reels can rotate freely.

  • As the handle continues to move the kicker, the kicker paddles push the discs forward briefly. When the handle is pulled back and the kicker has passed the discs, the bottom of the hook mechanism moves up against a slanted surface. The slant pivots the hook forward, which causes it to release the kicker.

  • The kicker spring jerks the kicker backwards at a good speed. The kicker paddles hit the notches on the discs, spinning the reels rapidly.

  • While all of this is happening, the control cam is slowly returning to its original position. When it does return, it pushes the cam plate back, which releases the stoppers. The different catches holding onto the different stoppers are positioned so that the cam plate will release the stoppers one at a time. Each stopper springs forward and locks into a notch, holding the reel in position.

In both types of systems, once the reels have come to a stop, the slot machine needs to read whether the player has won or lost. In the next section, we’ll examine some systems for making this determination.

The functioning of slot machines - An overview


  • There are dozens of different payout systems used in slot machines. In one of the simplest designs, a jackpot is detected by measuring the depth of notches in the discs that drive the reels. For simplicity’s sake, we’ll look at this sort of payout system in a bare-bones slot machine. The machine only accepts one kind of coin, and there is only one winning combination of images.

  • When you put a coin in this machine, it falls into a transparent case. The bottom of the case is a movable shutter that is connected to a metal linkage. Normally, the linkage holds the shutter closed. But when the machine hits the jackpot, the third stopper shifts the linkage up, opening the shutter so the coins fall out of the machine.

  • Each of the three discs has notches for each stop position of the reel. The notch for the jackpot stop is deeper than the other stops. Consequently, when the first reel lands on the jackpot stop, the first stopper moves farther to the left than it would for any other stopper. If the second reel stops on the jackpot as well, the second stopper also moves farther left. Same goes for the third reel and stopper.

  • But if only the second reel stops on the jackpot, the second stopper will not move into the notch. The first stopper has a catch that keeps the second stopper from moving past it. The second stopper, in turn, has a catch that holds the third stopper back. For the third stopper to lock into the jackpot notch, then, the first and second reels would have to have landed on the jackpot image. When this happens, the shutter opens to dump all of the coins that have been played since the last jackpot.

  • Typically, slot machines will have more elaborate versions of this design to pay out partially on certain combinations of images and payout completely on the jackpot combination.

  • In another popular system used in some electrical machines, the discs have a series of metal contacts attached to them. When the reels stop, one of the contacts engages a stationary contact wired to a circuit board. In this way, every stop on each reel will close a different switch in the electrical system. Certain combinations of closed switches (jackpot winners) will configure the machine’s electrical circuit to operate the payout mechanism.

  • A more advanced system uses photoelectric cells (also known as photodiodes), devices that generate a current when exposed to light, to detect the position. In this system, a series of holes are drilled through the rotating discs, all around their outer edges. The photodiode is positioned on one side of the disc, and a light source is positioned on the other side. As the disc turns, the light shines through the holes onto the photodiode. The pattern of holes in the disc causes the photodiode to generate a similar pattern of pulses of electricity. Based on this pattern, an electronic circuit can determine the position of the reel.

  • Newer slot machines use computers instead of gears. We will take a look at those next.

Modern computerized machines

The functioning of slot machines - An overview
  • Modern slots are more difficult to assess since the symbols and reels are programmed to the machine. It makes the games more versatile in a variety of respects. They are not limited, for example, to the size of the reels. Vintage mechanical devices could only have so many symbols on the reel until the game was practically and physically too massive to be realistic. But a computer-powered game could have 20 symbols per reel. Another advantage for manufacturers is that they can change the probability of a specific symbol showing up. Some symbols may turn up once every 10 spins whereas others may only come up once every 20 or 30 spins. It makes it possible for suppliers and casinos to sell more.

  • Also, the output of each pull is controlled by a central computer within the unit, not by the motion of the reels. The machine uses phase motors to rotate each reel and stop it at a predetermined point. Step motors are driven by short digital electrical pulses controlled by a computer, rather than by the fluctuating electrical current that drives the ordinary electrical motor. Such pulses shift the motor in a fixed phase, or stage, with great precision.

  • A Random Number Generator at the heart of the computer ensures that each pull has an equal shot at hitting the jackpot. Whenever the slot machine is turned on, the random number generator is spitting out whole numbers (typically between 1 and several billion) hundreds of times a second. The instant you pull the arm back (or press the button), the computer records the next few numbers from the random number generator. Then it feeds these numbers through a simple program to determine where the reels should stop.

  • Slots games are available in various denominations and have multiple features. You will enjoy pennies, nickels, dimes, quarters, and dollars. You will play games with five reels and 25 paylines. Scatter symbols, wild symbols, bonus games, and progressive jackpots add flavour and variety to these games. In the next section, we’ll see how the computer program can be configured to change the slot machine’s odds of hitting the jackpot.

The types of online slots

There are several various types of online slot games for players to take part in, as one would imagine, with so many online slot operators out there. These various types of games range from basic and reminiscent of the first machines players enjoyed during the early days of actual slot machines, to more difficult games that provide variants and the ability for even greater payouts.

Three-reel slots

The functioning of slot machines - An overview

These basic devices allow players to match symbols on the top, centre, or bottom rows to win with only three reels. Such games tend to have smaller payouts than their more complex versions.

Five reel slots

The functioning of slot machines - An overview

Compared to their three-reel equivalent, the big difference that five-reel slots have is that they open up the possibilities of items such as more pay lines, which in turn will open up the possibility of larger payouts. These five-reel games appear to be seen much more frequently than 3 reel slot games in progressive slots, and mega spin slots games.

Progressive slots

The functioning of slot machines - An overview

If other players could add to the jackpot that you could earn by playing online slots, wouldn’t it be great? This was the thinking process behind progressive slots, where for each spin made by all of the players of the game, jackpots rose by a tiny amount. Although there are slim chances of hitting the potentially big reward, they have the potential to be worth the risk.

Mega spin slots

The functioning of slot machines - An overview

Often, just one round of slots isn’t enough, a dilemma that mega spin slots can be the solution for. With super spin slots, players can play multiple slot games at once, all from the same screen at the same time, with the ability to win for multiple games at the same time.

Return to Player(Also known as RTP)

  • RTP stands for Return To Player which is a slot machine’s measured payout.
  • Online, it varies from 90-98% and in the land-based casinos, where there is less tight regulation on the slot machines, it may be anywhere from 70-92%. Therefore you have much more prospects to succeed when playing online. 
  • What we will always know, whether you play online or offline, is that the RTP will be less than 100%, as neither the casino provider nor the online casino would make any cash on it otherwise.
  • What does RTP say, then? The slot games are checked in particular software to achieve a mathematically accurate RTP, allowing several billion spins in a short time to be replicated. These spins determine the expected RTP. Unlike the real RTP, you have while you are playing.
  • After each session you play, the real RTP will change. The anticipated RTP is still going to be valid, but you will have to play billions of spins to get it.
The functioning of slot machines - An overview

Low and high volatility – Variance

Besides the RTP, in a slot game, it is the uncertainty that generates the charm. In a slot machine, uncertainty is the hidden element that makes it come alive. If properly used, it offers the best mix for the slot, to be fun and to provide the impression that a major win is just around the corner. Misused, you get flooded with a sense that the slot machine is an unlikely way to succeed at all.

What is the volatility distinction?

The variance chosen as high and low can be simplified as follows:

  • High variance slot-a lot of dead spins have a few wins, but you win it is big.
  • Medium variance slot – This is a combination of in-between high and low.
  • Low variance slot – Get a lot of wins, sometimes you won’t even win the bet back. There are zero or very few major wins.

All about the odds

  • In a modern slot machine, the odds of hitting a particular symbol or combination of symbols depends on how the virtual reel is set up. Each stop on the actual reel may correspond to more than one stop on the virtual reel. The odds of hitting a particular image on the actual reel depend on how many virtual stops correspond to the actual stop.

  • In a typical weighted slot machine, the top jackpot stop for each reel corresponds to only one virtual stop. For machines with a bigger jackpot, the virtual reel may have many more stops. This decreases the odds of winning that jackpot considerably.

  • The losing blank stops above and below the jackpot image may correspond to more virtual stops than other images. Consequently, a player is most likely to hit the blank stops right next to the winning stop. This creates the impression that they “just missed” the jackpot, which encourages them to keep gambling, even though the proximity of the actual stops is inconsequential.

The functioning of slot machines - An overview
  • A machine’s program is carefully designed and tested to achieve a certain payback percentage. The payback percentage is the percentage of the money that is put in that is eventually paid out to the player. The payback percentage in most casino machines is much higher than the minimum, often in the 90 to 97% range.

  • The odds for a particular slot machine are built into the program on the machine’s computer chip. In most cases, the casino cannot change the odds on a machine without replacing this chip.

  • There are several different payout schemes in modern slot machines. A standard flat top or straight slot machine has a set payout amount that never changes. The jackpot payout in a progressive machine, on the other hand, steadily increases as players put more money into it until somebody wins it all and the jackpot is reset to a starting value. In one common progressive setup, multiple machines are linked together in one computer system. The money put into each machine contributes to the central jackpot. In some giant progressive games, machines are linked up from different casinos all across a city or even a state.

  • Some slot-machine variations are simply aesthetic.

  • Video slots operate the same way as regular machines, but they have a video image rather than actual rotating reels. There are many reputed online casinos which offer video slots online to play with either for free or for real money.

15 secret slot tips that will really work wonders for you

The functioning of slot machines - An overview

Wrapping up

Even though the reels and handles in modern machines are completely irrelevant to the outcome of the game, manufacturers usually include them just to give players the illusion of control. These are only a few of today’s popular slot variations. Game manufacturers continue to develop new sorts of machines with interesting twists on the classic game. A lot of these variations are built around particular themes. There are now a variety of slots based on television shows, poker, craps and horse racing, just to name a few.


Are you less likely to win again after a major win or Free Spins?
No, that’s not how probability functions like. There is no memory for slot machines. The odds of winning are the same on any spin.
Can the RTP be updated by online casinos and slot providers?
This is not valid online, although it is possible at land-based casinos. However, a few online providers such as IGT used to have three separate RTP alternatives on their 92-96% slot launches, where the online casino could pick which variant they would like to bring live.
How are you going to win the slots?
Slots are random all together. So don’t expect any form of winning zig-zag technique to be discovered. Don’t think about where on the floor the games are placed. And please don’t think about whether you have a greater chance of winning by using the trigger instead of the spin button.
Any of those concepts are superstitions and/or theories. You should disregard them easily. The best advice we can give you to succeed at slots is to choose games that appear to be faster, boring, and play for higher stakes than you think you can.
Often, avoid slots, like those found in airports and pubs, with notoriously poor payback percentages.
Are slots online rigged?
They are not rigged. But the casino has an advantage at all times. Yeah, you do have a chance to win online slots. No, on every spin you’re not going to lose. And no, the game is not programmed by the casino to compensate for your last winning or losing streak.
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