A slot machine is a game of chance in which a random number generator decides each result and the reels display it. That has been true in principle since the 1980s, when computer chips replaced mechanical reels as the deciding mechanism, and it is true of every online slot today. This guide traces how slots developed from a Brooklyn poker machine in 1891 to Megaways and cluster pays, explains what is going on inside a modern game, and gives the practical tips that genuinely lower the cost of playing. For demo play, slot types and current bonus maths, see our free slots hub.
Slot: what is it?
A slot is a gambling machine, or its software version, that takes a stake, produces a random result and pays according to a paytable. The name comes from the coin slot on early machines; in Britain they are often called fruit machines, in Australia pokies, and in the United States one-armed bandits after the side lever of mechanical cabinets.
Every slot has three parts. First, the random number generator picks the result. Second, the maths model, designed by the studio, defines which results exist and how often each occurs, which sets the return to player (RTP) and volatility. Third, the presentation (reels, symbols, animations and sound) shows you that result. Players see only the third part, which is why slots feel more controllable than they are.
That simplicity is the appeal and the risk. No skill is needed, rounds take seconds, and the outcome is settled before the reels stop. Our article on why slots are so popular looks at the design reasons in more detail.
The history of the slot’s creation
The poker machine: 1891
Sittman and Pitt of Brooklyn, New York, built a machine with five drums carrying 50 playing cards. A player inserted a nickel, pulled the lever and hoped for a good poker hand. It had no automatic payout: bars offered prizes such as drinks or cigars. Two cards were often removed from the deck, typically the ten of spades and the jack of hearts, which roughly halved the chance of a royal flush.
The Liberty Bell: the late 1890s
Charles Fey, a mechanic in San Francisco, simplified the idea to three reels and five symbols: horseshoes, diamonds, spades, hearts and a cracked Liberty Bell. Because three reels with few symbols have a small number of combinations, the machine could pay coins automatically. Three bells paid the top prize. The Liberty Bell became the model for slot machines for decades.
Fruit symbols and the BAR: 1900s
As American cities restricted gambling machines, manufacturers such as the Mills Novelty Company added fruit symbols tied to chewing-gum flavours, presenting the machines as gum vendors. The BAR symbol is usually traced to the logo of the Bell-Fruit Gum Company. Cherries, lemons, plums, bars and sevens are still standard on classic slots.
Electromechanical slots: the 1960s
Bally’s Money Honey (1963 or 1964, depending on the source) used electrical circuits and a bottomless hopper that could pay up to 500 coins automatically. The lever became decoration; a button would do. Large automatic payouts made slots a mainstream casino game.
The video slot: 1976
Fortune Coin of Las Vegas built the first video slot, displaying reels on a modified 19-inch Sony television. It was first installed at the Las Vegas Hilton and, after approval by Nevada regulators, spread along the Strip.
Virtual reels and big jackpots: 1984 and 1986
Inge Telnaes patented a method that maps the result of a random number to “virtual” reel stops, far more than a physical reel can show. A jackpot symbol could now be rarer than its position on the reel suggested, which allowed far larger prizes. In 1986 IGT launched Megabucks, a progressive jackpot linked across many Nevada casinos.
Bonus rounds and online slots: the 1990s
Antigua and Barbuda passed legislation in 1994 that allowed licensed online casinos, and the first online casino software appeared the same decade. In 1996 WMS released Reel ‘Em In, credited as the first video slot with a second-screen bonus game. Free spins, pick-me features and multipliers followed.
Mechanics and regulation: 2010s to today
Studios added cascading reels, cluster pays and, in 2016, Big Time Gaming’s Megaways, where reel heights change every spin for up to 117,649 ways to win. Regulators responded to speed and intensity: in Great Britain, since 31 October 2021 at least 2.5 seconds must pass between the start of one online slot game cycle and the next, and autoplay is banned, and stakes are capped at GBP 5 per spin for players aged 25 and over and GBP 2 for those aged 18 to 24 (the GBP 5 cap applies from 9 April 2025, the GBP 2 cap from 21 May 2025).
| Year | Milestone |
|---|---|
| 1891 | Sittman and Pitt poker machine, Brooklyn |
| Late 1890s | Charles Fey’s Liberty Bell, San Francisco: the three-reel template |
| 1900s | Fruit symbols and the BAR (Mills Novelty, Bell-Fruit Gum) |
| 1960s | Bally Money Honey: electromechanical, bottomless hopper |
| 1976 | Fortune Coin: first video slot |
| 1984 | Telnaes virtual reel patent |
| 1986 | IGT Megabucks: wide-area progressive jackpot |
| 1994 | Antigua and Barbuda licenses online casinos |
| 1996 | WMS Reel ‘Em In: second-screen bonus round |
| 2016 | Big Time Gaming introduces Megaways |
| 2021 | UK online slot design rules (2.5-second minimum game cycle, no autoplay) |
| 2025 | UK online slot stake limits (GBP 5 for 25 and over; GBP 2 for 18 to 24) |
What happens inside a modern slot
When you press spin, the random number generator produces a number and the game translates it into a reel position for each reel. The result is final at that moment; stopping the reels early only changes the animation. A studio’s maths model then defines the probabilities: how many of each symbol sit on each virtual reel, what the features pay and how often they trigger.
Two numbers describe that model. RTP is the long-run share of stakes paid back: a 96% slot keeps 4% over millions of spins. Volatility describes how that return is spread, from frequent small wins (low) to rare large ones (high). Independent test houses check both before the game goes live, licensed casinos may only offer versions that have passed that testing, and regulators can ask for the test evidence at any time. In Great Britain, for example, operators must hold testing evidence for each game before release. Many games exist in several RTP versions, so the same title can cost more at one casino than at another.
Land-based and online slots compared
| Land-based slot | Online slot | |
|---|---|---|
| Result decided by | RNG inside the cabinet | RNG on the game server |
| Typical return | Set by local law and the operator; often lower than online | Usually around 94% to 97% for video slots; check the version |
| Free play | No | Demo mode on most games |
| Speed | Limited by the cabinet and local rules | Limited by regulation in some markets: in Great Britain at least 2.5 seconds must pass before the next game cycle can start |
| Jackpots | Standalone or linked across venues | Standalone, casino-wide or networked across many casinos |
| Information | Paytable on the glass, RTP rarely shown | Paytable, rules and usually the RTP in the info screen |
Online slots also keep a full history of your play in the account area, with every stake and win, which no cabinet offers. Reviewing it once a month is a simple reality check. The online version gives you more information than a cabinet ever did. Use it: the info screen is the one place where the slot tells you what it costs.
How to read a slot paytable
Open the paytable before your first spin. It answers four questions:
- Symbol values: what each symbol pays for three, four or five of a kind, usually shown as multiples of the total stake or the line stake.
- Special symbols: which symbols are wild and which are scatters, and whether wilds also pay on their own.
- Features: what triggers the bonus round, how many free spins it awards and whether it can retrigger.
- Maximum win: the cap on a single spin or feature, often stated as a multiple of the stake, such as 5,000x.
Below the paytable, the rules page usually shows the RTP and sometimes the hit frequency or volatility rating. If the RTP is missing or vague, treat that as a warning sign. A maximum-win cap matters too: a slot capped at 2,000x your stake cannot produce the life-changing prize its marketing suggests, while a slot advertising 50,000x will mostly pay far less than that, because such results are extremely rare.
Finally, check whether winning lines pay left to right only or both ways, and whether the game uses fixed lines or ways. Knowing the structure makes the result screen easier to read and spoils the illusion of “near misses”.
Slots guide: tips and strategy
No technique changes the outcome of a spin. The tips below change what playing costs you and how much control you keep.
- Check the RTP version. Open the game’s info screen. A 96.2% version costs a little less than half as much per euro staked as a 92% version of the same game (a 3.8% house edge against 8%).
- Choose volatility for your budget. A small budget on a high-volatility game often ends before a feature lands. Lower the stake or choose a lower-volatility game.
- Decide the session before you start: a money limit and a time limit. Use the casino’s deposit and session limits to enforce them.
- Calculate bonus wagering. Multiply the bonus (or deposit plus bonus) by the wagering requirement, then by the house edge. If that expected cost is larger than the bonus, you are paying to take it.
- Prefer wager-free free spins. Winnings paid as cash, even with a cap, beat a large match bonus with 35x to 45x wagering.
- Know the jackpot trade-off. Progressive slots fund the jackpot from the base game, so their RTP is often lower. Play them for the jackpot dream, knowing the price. Our guide to progressive slots explains how the pools work.
- Slow down. Fewer spins per hour means a lower hourly cost at the same stake.
- Never chase losses. Increasing stakes to win back money is the most expensive habit in gambling.
Slot myths and the facts
| Myth | Fact |
|---|---|
| A slot that has not paid for a while is “due” | Each spin is independent; the slot has no memory of previous spins |
| Casinos make slots tighter at weekends | The RTP is fixed in the certified game version; it does not change by the hour |
| Stopping the reels early improves the result | The result is decided when you press spin |
| Higher stakes improve the RTP | RTP is the same at every stake on almost all online slots |
| Free play mode is set to pay more | Reputable studios run the same maths in demo mode; check the RTP shown in the paid version |
| Near misses mean a win is close | A near miss is just another losing result |
Choosing a slot: a quick method
Pick a studio you trust (our gaming software hub lists licences and key games), open the slot’s info page and note the RTP, the volatility and the maximum win. Try it in demo mode for a hundred spins to feel the rhythm. Then decide a stake that gives at least 200 spins from your session budget. That simple routine avoids most expensive surprises, and it takes less than five minutes per new game.
Play responsibly
Slots are for adults only: 18+ (higher in some countries). If you notice yourself spending more or playing longer than planned, use deposit limits, take a time-out or self-exclude. Free, confidential help is available from the National Gambling Helpline (GamCare) on 0808 8020 133 in England and Scotland or 0808 2819 265 in Wales, or Gambling Therapy internationally. More tools are on our responsible gambling page, and general advice for every game is in our casino tips.
Frequently asked questions
Who invented the slot machine?
Charles Fey of San Francisco is generally credited with the modern three-reel slot: his Liberty Bell of the late 1890s paid coins automatically. An earlier poker machine by Sittman and Pitt (Brooklyn, 1891) came first, but paid its prizes over the bar rather than in coins.
Why are slot machines called fruit machines?
Early 20th-century machines showed fruit symbols, linked to chewing-gum flavours, partly to present them as vending machines where gambling was restricted. The name stuck in Britain, where “fruit machine” still means a slot.
Is there a strategy to win at slots?
No strategy changes the outcome of a spin, because a random number generator decides it. You can lower the cost: choose games with a higher RTP version, match volatility to your budget, read bonus terms and set limits.
Is there a best time to play slots?
No. Online slots have no memory and no schedule: every spin has the same odds whatever the time, day or recent results. Claims about “loose” hours are a myth.
How does a slot machine decide if you win?
The random number generator picks the result the moment you press spin, and the reels show it. The game’s maths, set by the studio and tested by independent labs, defines how often each result occurs.
What does RTP mean in slots?
Return to player: the percentage of total stakes a slot is designed to pay back over a very large number of spins. A 96% RTP slot keeps 4% on average, but a single session can end far above or below that.