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How Slots Work

For most players, playing slots is as complicated as feeding the player's card into the slot - or depositing into an online account - and slamming the 'Spin' button.

But behind the scenes there's a lot more going on.

Although technology has changed over the years, the idea is the same: the reels spin and the mechanism randomly stops the reels in specific positions to form winning (or losing) paylines. Winning combinations are then paid out to the players depending on the value of the symbols on the payline.

Mechanical Machines to Video Slots Revolution

Once upon a time, all slot machines in a casino were mechanical. Powered by levers and gears, a braking system stops the reels in motion, and sensors tell the machine what payouts are due depending on the symbols. Specially deep notches in the discs that controlled the reels would release a shutter inside the machine and pay out the jackpot if three or more were to line up in sequence.

Those machines have almost entirely been replaced with video slots powered by microchips, but the principal remains the same.

The advent of video slots meant that the mechanical cams, gears and kickers were replaced by microchips which controlled the whole process from the machine's motherboard.

After hitting the 'Spin' button (or pulling the lever on older and retro video slots models), the computer inside the slot machine selects numbers via the RNG (Random Number Generator).

Those numbers are then fed to the computer which correspond to symbols on the video slot reels. The slot - or computer - then spins the reels to the corresponding symbol and a combination or winning payline is formed. 'Step motors' inside the machine are used to physically stop the game at the predetermined, random, symbols.

Reels and Symbols

X include possible combinations of paylines etc on a typical 5-reel slot.

Random Number Generators

Because RNGs are powered by the computer, each and every spin is - or should be - totally random and separate from the next. There's no 'memory' with video slots, no 'jackpot waiting to be hit' after a barren spell; RNGs ensure that every spin is independent.

For online and land-based casinos, computer RNGs are tested independently by organisations like TST and eCOGRA.

Testing Labs and Audits

Testing labs work closely with software suppliers and manufacturers as well as regulators to ensure that slots are regularly maintained and standards upheld.

For a land-based slot, that means compliance testing on hardware AND software, jackpot controllers and Quality Assurance on electronic gaming devices. Testing labs also check machines as they're being developed before they hit the casino floor.

For online slots, that means evaluating Random Number Generators, game maths and payout verifications as well as the usual security and payout checks of the online casinos themselves. When reviewing UK casino sites we ensure that their games are deemed fair and accredited appropriately.

Controlling the Odds

One benefit of computer-powered video slots is that the payout frequencies can be controlled. Although it's true that slots are random, the way the reels and symbols are set up can drastically alter when a jackpot is going to be paid.

Some slots may carry lots of substituting Wilds, for example, while other games may have a meagre number of bonus icons. The chances, therefore, of triggering a bonus feature or jackpot, can vary drastically from machine to machine.

But the RNG also is programmed differently for how often those specific symbols are hit.

Let's say you're playing a 5-reel slot which has 20 symbols on each reel. However, the computer program is set so that each of those symbols will be hit with odds of 1 in 32.

You can see the number of 'virtual stops' is greater than the number of actual symbols, so the larger the virtual stops, the greater the chance you have of hitting a certain winning symbol. Of course, with more chances to hit, you also have a large chance of hitting a losing symbol too.

For a 5-reel slot, then, your chance of hitting that one jackpot symbol on each reel is 1 in 32x32x32x32x32 (32 to the power of five) = 1 in 33,554,432. Slots with bigger jackpots will have more 'virtual stops' and therefore the odds increase.

Understanding RTP (Return to Player Percentages)

Slots with a lot of virtual slots give players the sense they can hit the big jackpots but they also offer more ways to lose too. That means big-jackpot slots are called 'high variance' as they entice with lots of close wins but ultimately will dent your bankroll over the long-term until you hit that big jackpot.

Most slots, however, will have the RTP displayed in their paytables. These 'Return to Player Percentages' are the theoretical long-term payouts to players by a slot machine.

A slot may carry an RTP of 96% (common in online slots) which means that over the long term, for every $96/100 the machine pays out, $4 is withheld.

Laws govern the RTPs of slots, but land-based machines will usually sit around 85-90%. Online, however, the payouts rise - to about 95% on average.

Of course, just because a slot has a high RTP, it doesn't mean you're a winner straight away. You can hit a big winner on a low-RTP game if you're lucky just as you can a on a high-RTP machine; the question is when do you take the money and run?

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