Mechanical slots used to rule the roost at casinos the world over. But the advent of technology and the revolution in microprocessor power has led to even more powerful slot machines taking over the virtual and offline casinos.
It's hard to imagine that video slots have only been around for 40 years but today's games look a lot different to the first machines that appeared in Vegas casinos all those years ago.
And with the advent of mobile technology, video slots have entered a whole new phase.
Rather than mechanical reels overseen by an arm or any working parts to drive the action, video slots are powered by microchips and processors.
The action is presented on a video screen displaying the reels and paylines, with the betting action controlled either by physical buttons or a simple touchscreen.
Because of the power of the processors, video slots have developed to allow multiple paylines, changeable stakes, and bonus features to be included, giving the player so much more choice over their slots gambling.
The Las Vegas-based Fortune Coin company developed the first video slot in the mid-1970s.
Fortune Coin (named after its developer) featured a basic video screen which displayed the game - in fact, it was a 19" Sony monitor embedded in a slot machine cabinet. The game had a tentative launch, on offer at the Las Vegas Hilton, but it was an instant smash.
With a takeover from slots pioneers, IGT, the game enjoyed further success across Vegas casinos. But a sceptical public were only really won round once the format enjoyed success via video poker machines from Australian developers like Ainsworth and Aristocrat.
The Aussie pioneer, Aristocrat, through slots like Three Bags Full, started introducing multiple paylines into their games in the mid-90s and the notion that multi-payline video slots could be a winner took off.
Reel 'Em In, however, was the first video slot that included a bonus round played out on a separate screen.
Commonplace now, of course, but revolutionary then, WMS's game - released in 1997 - became the template for video slots for years to come. Featuring a fishy angling theme, Reel 'Em In machines featured classic symbols like BARs and gold 7s, and had hi-resolution screens to attract punters.
A faster processor in the game unit meant the gameplay was super-slick (for the time), and the game included a second-screen bonus feature where players had to fish for prizes.
The power of the technology in video slots means developers are able to cram more and more features into their games compared to old-school mechanical slots.
Here are some common features of modern video slots you'll find in a land-based casino or here at VegasSlots.co.uk:
Multiple paylines: A major advantage of video slots is the wide array of betting options the player has. Players can choose the number of coins to bet, the number of spins they want the game to automatically play ('Autoplay') and the number of paylines they want to play. Selecting the betting amount is as easy as touching the screen or slamming a button, while progressive jackpot hunters need just slam the 'Max. Bet' button to enjoy the most expensive action.
Scatter Pays - Scatters are symbols that pay out regardless of where they land on the reels. i.e. they don't have to be part of a winning payline to dish out cash. Usually in modern video slots, three or more Scatters on the reels in any position will trigger a special bonus feature.
Wilds - Wild icons replace any other symbol (usually except the Scatter or any bonus icon, however) to help reward extra cash wins. There's normally a jackpot for hitting five Wilds on a payline, while some developers have evolved the Wild feature to encompass 'Expanding Wilds' (stretching down to take up an entire reel), Replicating Wilds (substituting every symbol around them into extra Wilds) or random Wilds which land at different points on the reels.
Gamble Feature - An extra gambling feature on many slots lets you 'double' your win (or take away nothing) by selecting whether the next card shown will be red or black, or picking whether the next number shown on-screen is higher or lower than the last.
"Second Screen" Bonus Rounds - Perhaps the biggest advantage of video slots is the second-screen bonus. Most slots will feature at least one bonus round - normally triggered via the Scatters - and they can range from free spins to instant wins and 'Pick Me' bonuses (a second screen where the player chooses from hidden objects to reveal cash prizes).
More modern video slots will feature immersive gameplay where the player's position in the bonus 'storyline' can be saved and resumed upon playing the next time.
The advance of micro-technology in the 1980s led to the first RNGs (Random Number Generators) being designed for video slots.
With no moving parts, of course, video slots needed a way of ensuring every spin was random. RNGs - or 'Pseudo Random Number Generators' (PRNGs) - allowed manufacturers to 'program' a set of algorithms into games that would mean each spin was independent from any other.
Thousands of potential combinations are created every second by the machine's PRNG. Only when the player hits the 'Spin' button is a random number (the most recent random number created) chosen.
Of course, no video slot spin is truly 'random', rather the random number links to a certain set of stops on the reels. Over time, RNGs have advanced to ensure that the sequences of numbers chosen don't repeat themselves and give players too high an edge.
With the advance of technology, today's video slots allow for actual film-quality footage from Hollywood blockbusters and TV hits to be included in the game.
In turn this has led developers to sign deals with major film companies to bring out more and more branded slots.
Even on relatively inferior smartphones and tablets, powerful processors mean that even small portable devices can handle the software needed to power the newest video slots.
With attention-weary players after the next big thing, and developers keen to be original with every new game, the next generation of video slots is pushing the boundaries with more immersive gameplay, bigger jackpots and slicker graphics.
A new trend is even seeing 'skill-based' bonus features included in some games. Gambling is slowly being replaced by bonus features where the player's target skills or prowess on the sports field leads to big cash prizes. Whatever the future holds for video slots, there's no doubt that the days of the clunky, mechanical slot machine are over.