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How Do Slot Machines Work?

November 29, 2021

Slot machines. Fruities. Pokies. One-armed bandits.

Whatever you call them, it’s impossible to be even vaguely aware of the world of casinos and gaming without having come across a slot machine. From their origins in the late 1800s to their unprecedented popularity in online casinos today, slot machines have evolved into complex and interactive games with thousands of variations – though there’s still room in every casino for a classic one-armed bandit with three reels of fruits and bars and sevens.

But how do slot machines work? It’s a more complicated question than you might imagine. Let’s take a look at the original mechanical machines all the way to today’s modern online slots.

Slot machine mechanics

Classic slot machines, much like an automatic watch, are entirely mechanical. The original “one-armed bandit” machines use a system of gears and levers around a central shaft upon which the reels spin. When you insert a coin or token, a detector registers the payment with a sensor (much like a vending machine) and the lever can be pulled.

Many slot machines work this way even today. Once the lever is pulled, a series of gears begins to spin as a rotating piece in the mechanical setup (a cam) is moved forward at the same time that three paddles are moved towards the reels. The cam is spring-loaded to move back to its original position (which will stop the sequence) but the spinning gears delay this considerably.

The three paddles then make contact with the discs on which the reels are displayed, which are rotating around the central shaft. This causes them to spin rapidly until the cam has moved back into place, stopping each reel one at a time – this is not a mechanical necessity, but rather a way to build suspense for the player: have they won?

Have they, indeed? The three discs supporting the reels in a mechanical slot machine determine whether a payout is due by way of notches of various depths on the discs. Much like how a lock will only unlock when the correct key is inserted to push the lock gears into the correct position, a mechanical slot machine will only pay out when the notches on the gears line up correctly to release a certain number of coins.

The evolution of slot machines

While classic one-armed bandits, fruit machines and mechanical slot machines work their magic around the world still today, electrical slot machines are much more common in most casinos. From a player’s perspective, these slot machines work in the same way as their mechanical counterparts: players pull a lever and see the reels spin before awaiting the result.

Many electrical slot machines will still play a pre-recorded “clunk” of gears and levers falling into place, even though none are present! Instead, these electronic slot machines work by way of motors spinning the reels and electromagnets breaking circuits to stop the reels. When a winning combination is hit, metal contacts attached to the reels engage circuit boards that allow for different operations of the payout system to award different prizes.

Even these machines are now rare compared to computerised slot machines, which make up the vast majority of modern-day slots in casinos. While this might lead you to ask yourself “do casinos set slot machines”, these machines use computerised electrical impulses to spin the reels and an in-built programmed RNG (random number generator) to determine when to stop spinning. These RNGs are independently verified by third-party authorities to ensure that they are truly as random as can be. 

How do online slots work?

The next stage of evolution for slot machines was of course to step into the world of online casinos. Online slots are by far and away the most popular game at any online casino, and you’ll find thousands of different games programmed in their libraries. Much like computerised slot machines, they use an RNG to determine wins and can feature huge variety in bonus feature rounds and mini-games for players to enjoy.