Video slots are the most popular games in modern casinos. In the United States, more people play them than reel slots, video poker, blackjack, craps, or any other casino game. Online, all slot games are video slots by definition.
They are easy to play: choose how many paylines to activate, set a stake per line, and spin. But there are things worth understanding before you start:
- Results are determined by a random number generator. What you see on screen is a visual representation of an outcome that has already been decided.
- The house maintains its edge by paying winners at less than true odds.
- Nearly all video slots include bonus events as a primary feature, and those bonuses account for a significant portion of the game's overall return.
- Video slots put less of their payback into the main game than reel slots do.
Video Slots and Their History
Video slots have existed since the 1970s, but for a long time, players wanted nothing to do with them. The graphics were flat and low-resolution; the games used three video reels and came across as pale imitations of mechanical slots; there were no bonus events to set them apart; and players who had not yet grown up with home computers didn’t trust that the results were random. Mechanical reel slots are also computerised, and video slots used the same RNG technology, but that was not a distinction players were making at the time.
What changed was a series of breakthroughs, each one removing a barrier to acceptance:
- 1975: Fortune Coin Company introduces the first slot machine played on a video screen.
- 1979: SIRCOMA – later International Game Technology – launches the first widely accepted video poker game, setting the stage for video gaming in casinos.
- 1994: Bally Technologies introduces the Bally Game Maker, the first machine to put multiple video games on a single cabinet.
- Mid-1990s: Aristocrat Technologies in Australia develops five-reel games with free-spin bonuses. Success on the Pacific Rim convinces US manufacturers that video bonus slots have a future worth investing in.
- 1997: WMS Gaming releases Reel 'Em In, the first major video slot hit in the United States. Its success signals to the rest of the industry that the format has arrived.
From there, the innovations came quickly. Multi-tiered progressive jackpots gave players the chance to win amounts that mechanical reels could not easily deliver. Community-style machines added a social dimension.
Multiple bonus events within a single game meant there was always something new to anticipate. Licensed themes from television and film gave manufacturers a way to build bonus mechanics around familiar worlds. And improvements in animation and sound design gave video slots an entertainment value that mechanical reels could not match.
Video Slots and the Random Number Generator
Mechanical reel slots and video slots work the same way at their core: numbers selected by a random number generator are translated into the symbols that appear on the reels. The difference is in what those reels can do.
In a mechanical slot, the reel strip must fit inside the machine cabinet. That physical constraint limits how many symbols it can carry and how many combinations are possible. Video reel strips are virtual and can be as long as the programmer needs. The practical consequences are significant:
- Video slots almost always have more paylines than mechanical reel slots.
- They support more potential winning combinations.
- They can carry bonus events that must be factored into the overall game maths.
- They put less of their payback into the main game, reserving a significant share for bonuses.
With five reels each carrying 100 symbols, the number of possible combinations per payline is 100 × 100 × 100 × 100 × 100 – 10 billion possibilities. That’s the design space a video slot programmer works with, large enough to balance multiple simultaneous wins, scatter pays, bonus triggers, expanding wilds, and every other mechanic the format allows.
A few things hold true across virtually all video slots:
- You don’t need a winning symbol on every reel. Games pay for combinations starting from reel 1 across reels 2 and 3, with bigger payoffs for extending to reels 4 and 5.
- Some winning combinations pay less than the total bet. A combination paying five coins on a 20-coin bet is a net loss on that spin, but it contributes to a high hit frequency that keeps the session feeling active.
- Payoffs are proportionate to bet size, with no bonus for betting the maximum on most games.
Wild Symbols
A wild symbol substitutes for any other symbol on the reels, usually excluding scatter and bonus symbols. When a wild lands on a payline, it completes combinations that would otherwise fall short.
Expanding wilds go further: when a wild lands, it expands to fill all three positions in its reel column. With two expanding wilds on a five-reel game, every payline crossing those columns now has wilds in both positions, which can turn a modest spin into a significant one.
Scatter Pays
Scatter symbols pay regardless of where they land. Unlike standard winning combinations, they don’t need to line up on a payline from left to right. Three scatter symbols anywhere on screen are enough to trigger a payout or launch a bonus event. In many games, the bonus symbol and the scatter symbol are the same thing.
Bonus Events
Bonus events are a defining feature of the format. Free spins, pick'em bonuses, and wheel spins all fall into this category. On many video slots, roughly one third of all payback comes from bonuses rather than the base game – a game returning 90% overall might return only 60% on the base game and add 30% through bonus play. That proportion varies by game and manufacturer, but it must be accounted for precisely in the game's maths and random number sets.
Many video slots now carry multiple bonus events within a single game. The appeal is partly about the prizes and partly about anticipation. There’s always something new that might be around the next spin.
Paylines, and Slots Without Paylines
How Traditional Paylines Work
On a three-reel mechanical slot, the most common configuration was one line down the centre. When five-reel video slots broke through in the 1990s, early games added four more lines – three horizontals, a V-shape, and a chevron – for a total of five. From there, paylines expanded and began to zig-zag across the reels in increasingly complex patterns. Today, 20-, 25-, 30-, and 40-payline games are all common.
What Multiple Paylines Do
Multiple paylines open the possibility of winning on more than one line in a single spin, give designers flexibility in setting game volatility, make high hit frequencies achievable, and give players a wide range of betting options.
The volatility point is significant. With billions of possible five-reel combinations to work with, designers can distribute wins in many different ways. Frequent small wins at high frequency produce a low-volatility game that extends sessions. Focusing returns on bonuses and larger payouts produces higher volatility, a better shot at significant wins, but also a faster bankroll drain when those wins do not come.
Betting the Lines
On nearly all video slots, payouts are proportionate to the number of coins wagered per line, and winning combinations are equally likely to land on any payline. Covering more lines means more frequent wins, but those wins are smaller relative to the total stake. The payback percentage per coin wagered stays the same either way.
A straightforward example: on a 20-line machine where a combination pays five coins and occurs once per 100 plays per payline, betting one coin on one line returns five coins per 100 spins on 100 coins wagered, or one coin per 20. Betting one coin on all 20 lines returns 100 coins per 100 spins on 2,000 coins wagered – also one coin per 20. The hit frequency is higher when you cover all lines, but the long-run return per coin is identical.
Forced Bet Machines
When penny slots became the dominant format in the 2000s, operators needed players to bet enough per spin to keep games viable. The answer was the forced bet machine, which requires covering all paylines. On a 40-line forced bet game, the minimum bet is 40 credits, one per line. Players can increase the stake per line but cannot reduce the number of active lines.
243 Ways to Win (Reel Power)
Aristocrat Technologies developed a format called Reel Power in which players buy reels rather than paylines. It has proved popular enough that nearly every manufacturer now offers their own version, most commonly called 243 ways to win.
In Reel Power games:
- Winning symbols must appear on adjacent reels from left to right, as on a standard payline game.
- Winning symbols can land in any position on the reel: top, middle, or bottom all count.
- With all five reels active, this produces 243 possible winning combinations per spin.
Aristocrat also produces a four-row variant called Xtra Reel Power, which increases the number of ways to win to 1,024. Reel Power games typically use free spins as their bonus event and tend toward the more volatile end of the spectrum.
Cascading Reels
In cascading reel games, each symbol is an individual tile. When a winning combination lands, those symbols are removed, and new ones fall from above to fill the gap without an additional bet. If the new symbols form a winning combination, those are removed too, and the process continues until no new combination appears.
A small initial win can build into something much larger through a chain of successive pays. The tradeoff is a higher proportion of losing spins, making cascading reel games more volatile than most standard video slots.
Hit Frequency vs. Payback Percentage
Hit frequency is the proportion of spins that return any payout. Payback percentage is the proportion of total wagers returned to players over time. These are related but not the same.
A game that pays on more than half of all spins is not necessarily a generous game. If most of those pays are smaller than the bet, the payback percentage can still be modest. Conversely, a game that pays infrequently can have a higher payback percentage if its larger wins are substantial enough. The distribution of return matters as much as its frequency.
How Designers Control Hit Frequency
On a video slot, designers can put any number of any symbol on each reel, and that number can differ from reel to reel. This is the primary tool for controlling hit frequency without changing the pay table.
Consider a simplified game with 30 symbols per reel and 2.43 million total five-reel combinations. The game pays for two or more matching symbols in a row from reel 1.
In a high-frequency design, five of a given symbol on reel 1, four on reel 2. That gives 20 two-symbol combinations, roughly once per 45 spins. Hawks thin out on later reels: three on reel 3, two on reel 4, one on reel 5. That gives 120 five-symbol combinations out of 2.43 million or, approximately, once per 20,250 plays.
In a lower-frequency design: two symbols on reel 1, three on reel 2 – only six two-symbol combinations, once per 150 spins instead of once per 45. Three on reels 3 and 4, five on reel 5: 270 five-symbol combinations, roughly once per 9,000 plays.
Same pay table. Only the symbol distribution has changed. But the play experience is completely different: the second design pays less frequently at the low end and more at the top.
Entertainment Games vs. Gambling Games
Casino professionals distinguish between two types of video slot, and it’s a useful framework for players.
Entertainment games have high hit frequencies and modest jackpots. They are designed for extended sessions with frequent, smaller returns that keep the bankroll relatively stable. Pick'em bonus events are characteristic of entertainment games.
Gambling games offer larger jackpots and bigger potential wins at the cost of lower hit frequency. When the wins come, they can be substantial; when they don’t, bankrolls drain faster.
Signposts of gambling games include large jackpots, stacked symbols, where the same symbol fills multiple reel positions, enabling big wins across many paylines simultaneously, and free-spin bonuses as the main or only bonus event.
These are guides, not rules. Many games blend elements of both, and understanding how to win at slots starts with knowing which type you're playing. If a game is not delivering the kind of session you’re looking for, moving to a different one is always an option.
Key Takeaways
- Results are determined by a random number generator; wilds and expanding wilds complete winning combinations.
- Scatter pays and bonus events (free spins, pick'em, wheel spins) account for roughly a third of total payback on many games.
- More paylines mean higher hit frequency, not higher payback per coin; forced bet machines require covering all lines.
- 243 ways to win and cascading reels are alternatives to the traditional payline format.
- Hit frequency and payback percentage are controlled independently, via symbol distribution across reels.
- Entertainment games (high frequency, modest jackpots) vs. gambling games (low frequency, big jackpots).
FAQ – Video Slots
How do video slots work?
Video slots use a random number generator to determine the outcome of every spin. The numbers are translated into the symbols shown on screen. The spinning reels represent an outcome already decided, not the mechanism producing it.
What are paylines in slots?
A payline is a defined path across the reels along which winning combinations are evaluated. Traditional video slots offer between 5 and 40 paylines, and winning combinations must land on an active line to pay, except for scatter symbols, which pay regardless of position.
What does a wild symbol do in a slot machine?
A wild symbol substitutes for other symbols to help complete winning combinations, usually excluding scatter and bonus symbols. Expanding wilds grow to fill an entire reel column when they land.
What is hit frequency in slots?
Hit frequency is the percentage of spins that produce any payout. It does not indicate payout size. A game can have a high hit frequency and a modest payback percentage if most wins are smaller than the bet placed.
What is the difference between entertainment and gambling slots?
Entertainment slots offer frequent small wins for extended play. Gambling slots offer larger jackpots with lower hit frequency, meaning bigger potential wins but faster bankroll swings.
