Home / Blog / How Do Slot Machines Work

How Do Slot Machines Work

How Do Slot Machines Work

Table of Contents

How Do Mechanical Slots Work?

For those who don’t know, mechanical slots were the mainstay when slot machine games were introduced to the world. Think of the Liberty Bell slot by Charles Fey, introduced in 1894. This classic 3-reel slot was a mechanical slot with 3 spinning reels. It included rudimentary symbols such as hearts, diamonds, and spades, and a cracked Liberty Bell. When players were fortunate enough to land 3X Liberty Bell symbols on the middle payline, a jackpot prize of 10 nickels was awarded to players.

Mechanical slots were made from cast iron. Three metallic hoops a.k.a. spinning reels featured 10 symbols apiece. Players pulled the lever which spun the reels. Once the reels stopped spinning, payouts were awarded if players landed 3 identical symbols on an active payline. The machine dispensed winnings into the coin tray. Remember, with mechanical slots the actual reels and all the symbols on those reels must fit within the physical casing of the machine. This limits the number of symbols, paylines, and possibilities.

The truth about how slot machines work is pretty cut and dried. Mechanical slots require players to deposit coins. Once the coin has been accepted, a system of levers, spring-loaded slides, hammers, cogs, dials, and other components interact to provide as random-an-outcome as possible. For a real-time visual of the deposit, spin, and result process of mechanical slots, take a look at the following YouTube video on mechanical fruit machines, a.k.a. fruit slots. These were known as one-armed bandits, since you pulled the lever to generate a spin result!

How Do Computerised Slots Work?

As you can imagine, the physical limitations of traditional mechanical slots were extremely restrictive. For starters, the slots casing unit is only so big, and can only accommodate a set number of reels, symbols, and paylines. Enter the era of computerised slots. Nowadays, the vast majority of slot machine games use computerised mechanisms, rather than the mechanical parts of the pioneering slots. With computerised slots, outcomes are governed by RNGs – Random Number Generators. The moment a slot machine game is turned on, powerful randomising software creates innumerable random outcomes for each of the reel positions that can land on a given spin.

As an example, imagine that 1000 outcomes can be generated per second on a computerised slot machine game. If there are 5 reels, each RNG outcome must generate results for reel 1, reel 2, reel 3, reel 4, and reel 5. At the precise moment that you click the spin button, or pull the lever, the computerised slot machine game locks in an RNG-generated outcome. What you actually see on your screen (spinning reels with symbols coming to a stop) is merely done for entertainment value, since the outcomes are instantly known by the computer. Imagine how boring slots would be if results were immediately displayed on screen the second you click the spin button?

From an audio-visual perspective, computerised slots look and feel identical to old school mechanical slots. Truth be told there aren’t any mechanical spinning reels on computerised slots – everything is digital. Each of these slot machine games has a computer chip which is pre-programmed with RNGs and RTPs. The RTPs are the return to player percentages which indicate the long-term return to player for every £1 that is wagered. For example, a slot machine game with a 97% RTP will pay back 97p on every £1 over the long-term. It is a theoretical concept that simply doesn’t hold true over the short-term. In fact, anything can happen on any given spin. That’s why slots are so appealing to players.

The RNGs in computerised slots mimic lady luck as best as possible. Outcomes are random, since there are no discernible repeating patterns in the algorithm. The probabilities of winning a jackpot, or a small cash prize are based entirely on the probability of landing a set number of symbols in combination, relative to the total number of possible symbols on the reels. Put differently, the scarcer the symbols, the higher the payouts will be when the right combination of those symbols land. Consider a 3-reel slot with 10 symbols on every reel. Perhaps 5 of them are cherries, 3 are bananas, and 2 are bells. The rarest symbol – the bells – will pay the most when 3 of them land on active paylines on each successive reel. Expect medium-sized payouts with bananas, and low-value payouts with cherries.

Can You Cheat Slots Machines?

By cheating, we are alluding to the manipulation of slot machine games to be favourable to the player. Whether you’re playing online slots or land-based slots, it is exceptionally difficult to cheat slots games. That’s not to say that cheating is impossible. Since slots are governed by random number generators, shady programmers and hackers are always on the prowl. As alluded to earlier, random number generators are governed by algorithmic codes to randomly generate outcomes for slot machine games. If that algorithm is known, and variance and volatility can be determined, it is theoretically possible for a scammer to create a program that can anticipate slot machine outcomes.

The degree of sophistication required to do something on this scale is beyond the comprehension level of 99% of slots players. So, while it is certainly possible to cheat slot machines by manipulating their computer chips, or tampering with their functionality, this is a rarity. Over the years, various criminal syndicates have attempted to win big payouts by cheating slot machine games. Our guide on how slot machines work is not about reverse-engineering RNGs to better understand the probabilities of winning combinations. Rather, we focus on the actual functionality of these games, whether they are mechanical slots, or computer slots.


Today, we have learned how mechanical slots work, and how computerised slot machines work. There are different systems at play in each case. With a mechanical slot machine game, it’s relatively easy to answer the question: How slot machines work? There is a system of physical reels encased within a slot machine body. A player pulls the lever which then activates a series of springs, cogs, teeth, reels, slides, leavers, and hammers. Whenever winning symbols line up in combination on each reel, that immediately fulfils the criteria for coins to be dispensed.

Computerised slots don’t have physical reels and symbols painted on them. Rather, these are electronic elements which are governed by computerised chips with RNGs (random number generators), specific RTPs (return to player percentages), and variance/volatility. The RNGs produce thousands of outcomes within double-quick time, and the moment you click the spin button, or pull the one-arm bandit, the RNG result is locked in. Values are assigned to each reel and symbol on each reel, and the result is displayed once the reels come to a stop.

If you have a small budget, you should play low-volatility slot machine games and enjoy more of your favourite slots for longer. If you have a big budget and you’re a gambler, you probably want to play high volatility slots where the possibility for winning big exists, albeit infrequently. Criminals routinely try to cheat at slots. With the right technical expertise, insider information, and access to slot machine game mechanics, some even pull it off. Over the years, various high-level syndicates have been caught cheating slot machine games at casinos. These scammers typically win small amounts, to guard against being flagged by the casino. Cheating is illegal, and punishable by fines and/or imprisonment.