How Video Slots Work: Complete Guide

  By benboland – Last updated 18 Jan 2022

We understand that many of you love to play online slots for a chance at monumental payouts. Nowadays, though, slot games have evolved past the point of a generic structure, and the inner workings of any release can vastly differ from one game to the next. Therefore, we have compiled an informative guide to playing video slots, which you’ll find below, so you are fully aware of what happens each time you play!

What Is A Slot’s Random Number Generator for Video Slots?

A Random Number Generator (RNG) is a means to create a random result from a range of values. In terms of its role in video slot gameplay, it’s how a game randomly determines the outcome of each spin and whether it results in a win or a loss, whilst factoring in other variables such as hit frequency and return to player percentages.

The thing is, Random Number Generation can be broken down into two distinct categories: True RNG and Pseudo RNG. True Random Number Generators, used in vintage or mechanical slot machines, incorporate entropy to deliver authentic results – we’ll cover this in greater detail further in our guide. Pseudo RNG, however, which is used in all digital or online slot games, is not affected by natural entropy.

Pseudo Random Number Generators

Pseudo RNG, or PRNG, must compensate for the lack of entropy to simulate authentic randomness. To do so, results are drawn from a short initial value going through a complex equation to deliver outcomes with no predictable patterns. To reach this level of randomness, a microprocessor constantly generates results, even when you’re not playing – it doesn’t just begin the computation whenever you hit the spin button!

As you’d expect, it’s a complicated process and one that cannot be explained without first understanding certain factors. So to help you gain further insight, we’ve gone into greater detail below.

How Does Rng Work?

RNG is the cornerstone of modern slot gaming. In the early days, physical slot machines used mechanical concepts to deliver randomisation. Now, with the new wave of online casino gaming, the entire process has been digitised via the use of microprocessors.

As you’d imagine, RNG has one goal: to generate random numbers. What you might not realise, however, is that video slots do this constantly. The microprocessor generates a new set of random numbers in a fraction of a second, constantly repeating the process whether the game is being played or not.

So, what happens when you hit the spin button? Well, it’s important to understand that the entire process is completely separated from the game itself. The RNG supplies the game with a random number and the game then expresses it in a specific format – in this case, a series of slot symbols, which either result in a winning combination or a loss.


Seeds, or keys, are what determine the results of digital slots and are the base value of pseudo-random number generation algorithms. As we’ve previously mentioned, the RNG process constantly occurs, and what you see when you hit the spin button is the result of a complex process that begins with a seed. This is an initial value that undergoes a series of computations to yield a final result – what you see on the reels.


Entropy is a scientific term that refers to a lack of order or predictability. So as we’re sure you can surmise it plays a major role in video slots, but it’s in the form of simulated entropy or simulated randomness as it were.

The major factor here is that video slots do not have access to physical hardware to create results with natural entropy. Instead, the seed that is generated for the PRNG sequence uses simulated entropy to create a random key for the algorithm to produce the end result.

Ultimately, it’s a way for video slots to generate unpredictable results, thus closing the door to those with malicious intent who wish to exploit the game’s outcome.

Computational Generation Methods

When it comes to video slots, extremely long and complicated equations are required to create the random number sequences, as opposed to individual numbers, that determine the outcome of each spin. When these sequential number results are provided, the information is translated to what you see on the screen – each symbol, its positioning and whether or not these elements combine to create a win.

Computer languages such as PHP and Python are commonly used to generate these statistically random results using pseudo-random number generation. 

What Is Return To Player?

Return to Player, or RTP, is a key factor you must consider when figuring out how to win at video slots. Each game will have a specific return to player rate, expressed as a percentage, that you can use to gauge your estimated returns when playing online slots.

This is only an average however and it does not convey the exact amount you will win. The figure derives from billions of simulated spins and it will deviate during your play session, sometimes favourably and on other occasions not so much. In short, you’ll stand a better chance of winning if you look to play games with higher RTP rates.

Check out our dedicated page for more details about RTP and what it means.

What Are Paylines In Video Slot Machines?

how video slots work question

The layout of most modern video slots revolves around a traditional payline structure. These are specific patterns that run across a varying number of reels that yield payouts whenever the appropriate number of matching symbols appear in the correct positions, adjacently, diagonally or in some cases by following a set pattern.

Generally, the more reels and rows a video slot has, the more active paylines there are available. Classic 3-reel slots often utilise 9 paylines and standard 5-reel slots often have between 10-20 paylines. However, recent innovations in video slot gaming have produced games with 6+ reels and hundreds of thousands of paylines, although not necessarily in the traditional format – they’re often described as Megaways or Ways to Win.

It’s important to remember though that, at least normally, whenever you select your stake, it’s based on the number of paylines, so the more that there are, the larger the bet value is likely to be. Furthermore, you’ll want to check to see if your chosen video slot comes with fixed or variable paylines, as this can impact how the gameplay unfolds.

Fixed Paylines

By default, most online slot games come with fixed paylines. This means that whenever you spin the reels you’re betting on every possible combination of winning symbols and you needn’t worry about selecting each payline individually. As such, your overall wager is automatically determined by multiplying your line wager with the number of available paylines. For example, if the video slot had 20 paylines and your total stake was £1, you’d effectively be betting £0.05 on each payline.

Also, with every payline activated you needn’t worry about missing out on potential bonus features if the necessary symbols were to land in inactive positions, as every reel and symbol position is active on every spin.

Variable Paylines

With variable paylines, you have more control over the gameplay. You get to pick which paylines are active and how much you want to bet on each, which is reflected by your overall stake per spin.

Surely by choosing to play fewer paylines you’re reducing your chances of winning though, right? Well, you are limiting your chances of landing a winning combination by not playing all of them but it’s a matter of risk versus reward. Your line bet will remain consistent, along with the respective symbol values. Therefore, by playing fewer lines any win that lands effectively holds a greater value. However, the obvious downside to this tactic is that you’re decreasing your chances of those combinations landing.

That being said, there are specific examples of where this can be used to great effect. Certain video slots still allow you to trigger various bonus features even if you don’t play every payline. So, if you’re feeling particularly lucky, you can take your chances of triggering a potentially lucrative feature at a reduced cost per spin.

How Do Video Slot Paylines Work?

Before we go into our explanation of how paylines work we must make several distinctions. Not every slot game has traditional paylines. Many modern releases utilise alternative mechanics such as Ways to Win, Megaways and Cluster Pays to deliver their respective game’s payouts. With these, you’re no longer restricted to landing specific symbol combinations in exact positions and patterns. Instead, more options become available that will generate a successful win. Below, we’ve concisely outlined how each of the mechanics works.

  • Traditional paylines: These require matching symbols to land in exact positions to follow a set pattern on adjacent reels. You’ll typically need 2-3 matching symbols to appear starting from the leftmost reel to trigger a winning combination.
  • Ways to Win: Again, you’ll need to land matching symbols to land on adjacent reels to form a win. However, the difference here is that you’re not restricted by a set pattern. As long as you land the minimum number of required symbols in any position on consecutive reels you’ll trigger a payout.
  • Megaways: Megaways are Big Time Gaming’s innovative payout mechanic found in a myriad of licensed online slot releases. This works the same as Ways to Win but there are typically a greater number of reels available.
  • Cluster Pays: This mechanic is often used in grid-style video slots. As opposed to needing to land matching symbols on adjacent reels, here you must form a cluster of matching symbols anywhere on the grid – the larger the cluster, the greater the payout.


Most slots are designed to award payouts starting from the leftmost reel. Traditionally, that means you must land matching symbols on at least reels 1, 2 and 3 to form a winning combination. With the introduction of modern slots though, that doesn’t mean they necessarily have to be in a horizontal line, many paylines now award payouts diagonally and even vertically.

Additionally, certain releases have introduced the Pay both Ways mechanic, which enables payouts to be awarded starting from the rightmost reel provided enough matching symbols appear – NetEnt’s Starburst is a prime example.

Wild Symbols

links of ra screenshot
A Wild as seen in the Links of Ra slot

Wilds are additional symbols that substitute for all regular paytable symbols to help form winning combinations. For example, if you had 4 matching symbols on a payline on reels 1, 2, 4 and 5 this wouldn’t result in a payout. However, if a Wild Symbol were to land in the correct position on reel 3 it would complete the combination thus triggering a sizeable win.

That’s not all these special symbols can do though. With many video slots, the Wild can provide additional benefits to further improve your payout potential. You’ll often see Multipliers attached to these symbols that vastly increase your overall win when they form a win. Additionally, other video slot releases incorporate mechanics such as Sticky Wilds and Walking Wilds to bolster your chances of winning substantial amounts – these are often only present within a slot’s bonus feature, though there are cases where they’re utilised in the base game so be sure to keep an eye out for them!

Scatter Symbols

Scatter symbols are typically your path to a thrilling assortment of bonus games and free spin features. These often pay and/or trigger various features irrespective of their position on the reels – you won’t normally need to land them on a specific payline. However, there is usually a minimum number of symbols you’ll need to land to activate certain features.

They’re not always attached to a slot’s bonus round though. In some cases, they are merely special paytable symbols that award sizeable payouts regardless of where they land.

Bonus Symbols

Similar to Scatters, Bonus symbols can trigger a wide range of unique features. When the required number of symbols land during a single spin, the game will often transition to a new screen where plenty of free spins, multipliers and other lucrative mechanics await.

Paylines Vs Reels

buffalo ways screenshot

Certain terms within the online casino industry can be rather confusing to newcomers. When playing video slots, you’ll come across two such terms, “Reels” and “Paylines”, in almost any situation and it’s important to understand the differences between them. A screenshot from Buffalo Ways is a good example.

Reels are the vertical strips containing the slot’s paytable symbols that revolve each time you hit the spin button. The number of reels will often differ from one slot to the next based on the developer’s choice of theme and design. Generally, most modern slots adopt a 5-reel layout yet there are many that employ a classic 3-reel approach and others that introduce 6 or more. It’s always a good idea to take a look at the information tab before playing to familiarise yourself with the rules. Alternatively, you can check out our slot reviews for even more information!

The term “payline” refers to an active line or pattern that you must land matching symbols upon to receive a payout. These typically start from the first reel, with each subsequent position following a set pattern on adjacent reels either horizontally or diagonally.

Types of Jackpots in Video Slots

bonus generic1

If you’re looking to scoop immense prizes when playing video slots, your best course of action is to choose those that offer jackpots. Typically, when you think of the term “jackpot” you think of ringing bells and alarms signalling the payout of huge amounts of cash. Whilst this is true, not all jackpots are the same.

As you can imagine, your chances of landing a jackpot worth millions are extremely slim. There’s always a chance though, and if your stars align you could be walking away with a life-changing sum of cash. Not to worry though, other types of jackpots that are much more attainable for the everyday player, which we’ve outlined in detail below.

Fixed Jackpots

Fixed jackpots are game-specific prizes that are usually up for grabs via a selection of in-game features and/or bonuses. These jackpots will never increase in size, rather they remain at a fixed value at all times – even after they’ve been won.

The beauty of this type of jackpot is that most video slots that incorporate them offer them in multiple sizes – mini, minor, major and mega, with the latter being the most difficult to earn. The smaller prizes, however, are often much more attainable.

Progressive Jackpots

Progressive jackpots have a growing prize pool that increases each time a player places a bet on an eligible slot – we’re talking about huge prizes here. A small percentage of your wager is added to the overall value until the jackpot is won. It then resets to its initially seeded amount to begin its growth once more.

Local Jackpots

Local jackpots refer to huge prizes available at one specific casino, whether it be land-based or online. Eligible games draw a percentage of qualifying bets into a cumulative prize pool, which only players from that casino can win. There will usually be a list of eligible video slots that you must play to stand a chance to land this type of jackpot. Make sure to check which do so beforehand to avoid missing out on your chance to scoop a fantastic lump sum.

Network Progressive Jackpots

Network progressive jackpots are without doubt the most popular jackpot features available. This is due to their potential to reach astronomical figures; lucky players have won upwards of £10 million in the past.

The reason the prizes are so monumental though is because the overall prize pool is accumulated from eligible bets at participating casinos around the world. Therefore, you’ll be competing against thousands, if not millions, of other players when trying to trigger the assorted features that can deliver these potentially life-changing prizes. We have a great guide if you want to know more about progressive jackpots.

Best Video Slots

So, we feel as though it’s safe to say that’s everything you’ll ever need to know about how video slots work. We’ve covered all of the basics and then delved even further into some of the more intricate points to give you a precise analysis of what happens whenever you choose to play.

The next logical step in our journey then is to point you in the direction of the best video slots to play and where you can find them. Thankfully, you have a great number of casinos to choose from, each of which offers a diverse range of video slot builds, thrilling bonus features and immense jackpots.

With that in mind, we’d like to highlight STS Casino as a great place to enjoy all of the most popular slots whilst also getting a generous welcome bonus when you register.