If you have ever seen a row of slot machines in a casino or watched one in a film, you may have wondered what really goes on inside. Do these machines truly give out random results, or is there something more happening that meets the eye?
Many people are curious about the inner workings of mechanical slot machines and what determines the outcome of each play. This article breaks down how these machines operate, so you can understand exactly what happens if you press spin.
Let’s get started by looking at the basics behind these familiar machines and what makes each spin unpredictable.
How Classic Mechanical Slot Machines Work
Mechanical slot machines use a system of reels, springs, levers, and other physical parts. When you pull the lever or press the button, the reels begin spinning and stop one by one. Each reel is marked with a number of symbols, and the outcome is decided by where these symbols land.
A metal shaft runs through the centre of the machine and holds the reels in place. This shaft connects to a special braking system, which determines where each reel will stop. In older slot machines, notches and stoppers played a vital role in bringing the reels to a halt.
To help keep results unpredictable, some early machines used a part called a “randomising cam” or a metal stepper. These devices made it very difficult to predict which symbol would appear next.
The odds are calculated by the number of symbols per reel and how many reels are in play. For instance, with three reels and ten symbols on each, there are 1,000 different possible outcomes each spin. Every spin works independently, so the same chances apply every time.
As technology changed, many machines that still looked mechanical began using microchips and Random Number Generators (RNGs) within. Most classic machines, especially in the UK, are now quite rare, though you may spot one in a collection or as a decorative item.
Players should always remember to gamble responsibly and within their means- never wager more than you can afford to lose.
What’s Inside a Mechanical Slot Machine?
Taking a look inside reveals a collection of moving metal parts (and sometimes plastic). The reels, covered in symbols such as cherries, bells, or bars, spin around a central shaft.
Key Parts You’ll Find:
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Handle or button: Starts the reels spinning when activated.
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Springs, gears, and levers: Set the reels in motion and handle their stopping.
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Braking system: Made up of metal stoppers that decide where reels stop.
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Coin slot and tray: Accepts coins and pays out winnings.
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Payout mechanism: Releases coins when a winning combination appears.
Older machines checked coins using only mechanical levers, but modernised versions (and UK venues) use electronic sensors as well, making things more secure and reliable.
Classic mechanical machines do not include screens or computer parts found in today’s slots. Any information needed to play and understand the payouts can be found directly on the machine.
How Mechanical Slot Machines Create Random Outcomes
Mechanical slots use a range of springs, stoppers, and randomising devices to make sure outcomes can’t easily be predicted or repeated. Each spin is entirely separate from the last, and the result is determined by the stopping position of the spinning reels. With three reels containing ten symbols each, for example, you have up to 1,000 possible outcomes per spin.
Early machines used randomising cams and weighted reels. While these don’t match the precision of modern digital RNGs, they still made it very hard for anyone to anticipate outcomes. Developers designed these mechanisms to stop patterns from forming and to keep every spin uncertain.
Today, almost all slot machines in the UK use digital random number generators for increased security and fairness. There may be a few places where traditional mechanical slots are found, but these are now a rarity.
Mechanical Slots vs Digital and Online Slot Machines
Mechanical slot machines and digital slots differ both in structure and in how game results are decided. Mechanical machines rely on spinning parts and physical mechanisms, limiting the number of possible outcomes to what fits on the reels.
Digital slots, including those commonly featured in the UK and online, use computer software and a rng. This RNG instantly creates one of millions of possible outcomes for every spin, making it impossible to predict the result.
Digital slots allow for:
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Many more reel symbols and bonus features.
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Several paylines and extra features like cascading reels or Megaways.
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Information such as Return To Player (RTP) rates and volatility to be displayed up front.
While mechanical machines limit wins by the physical number of symbols and coins they can hold, digital slots offer a very wide range of options and features. If you need more detail on how RTP and game mechanics work, you could check the relevant game’s help section online or refer back to the information about RTP and volatility.
When choosing between mechanical and digital slots, consider what sort of game features and experience you most enjoy.
How Payouts Work in Mechanical Slot Machines
Every mechanical slot includes a paytable. This shows the symbols, their combinations, and payout amounts. Line up the right symbols as shown on this paytable, and you will receive a payout.
The payout mechanism, housed inside the machine, automatically releases the correct number of coins into the tray after a win. Payouts are linked to the symbol combinations and the coins entered to play. Mechanical slots often only take coins and can only pay out as much as they can physically store.
A single mechanical slot may have one payline or a few. The most valuable wins often come from lining up rarer symbols, such as bars or sevens, across the main payline. Unlike digital machines, mechanical slots rarely display RTP or similar statistics clearly. However, each spin is independent, with thousands of combinations possible, ensuring outcomes stay uncertain.
If you need a reminder about finding rules or paytables, everything is set out on the machine itself. Checking these before playing could help you know what to expect when spinning the reels.
How Cheating was Prevented in Mechanical Slot Machines
When first introduced, mechanical slot machines were open to certain cheating tricks. Bent coins or “slugs” and the “string trick” (threading a coin on a string to claim credits or retrieve your stake) were some of the best-known methods. There were even attempts to manipulate the payout mechanism directly using thin tools.
Casinos and slot makers soon responded, developing coin detection devices and upgrading the construction of machines to prevent tampering. These solutions quickly became standard in UK casinos, making cheating very difficult.
Advances in both mechanical and digital machine security now provide much greater protection. All machines found in licensed UK venues must meet UK Gambling Commission (UKGC) rules and are carefully regulated to make sure every game is fair and safe for players.
Where Mechanical Slot Machines are Found in the UK
Mechanical slot machines have mostly disappeared from UK casinos and are rarely in use today. Most venues now feature digital and electronic slots, which offer more choices and security for players and operators.
Occasionally, you might spot a mechanical slot in a small arcade, private collection or as a showpiece in a casino, but they are mainly seen as collector’s items or displays. Finding a machine that is available to play is unusual, and most UK players will now be using digital slot machines if they play in a casino.
Online casinos in the UK are fully digital and do not include mechanical slots, but some online games are designed to look just like the classics — players get the look and feel, with the security and features of modern digital slots. The game libraries in most online casinos make it simple to find a style of slot that fits your budget and your preferences.
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**The information provided in this blog is intended for educational purposes and should not be construed as betting advice or a guarantee of success. Always gamble responsibly.
*All values (Bet Levels, Maximum Wins etc.) mentioned in relation to these slot games are subject to change at any time. Game features mentioned may not be available in some jurisdictions.