When compared to the overall history of gambling, the history of slot machines is quite short. Because of the efforts that their inventor made - a car mechanic called Charles Fey - slot machines made their first appearance in the year 1894. The very first slot machine that is known as the prototype of today's modern slot machines was given the name "The Liberty Bell". Today, this slot machine can still be found on display inside a restaurant in Nevada.
Back in the 1930s, slot machines started to appear in the scene of gambling in Western America and in the 1940s, they could be found in casinos all over Las Vegas, thanks to gangster Bugsy Seigel's efforts. As of the 1990s, these slot machines started to get even more popular compared to table games and since then, they have taken over the whole industry of casino gambling, which accounts for most of the revenue that casinos all over the world earn.
In essence, slot machines online are merely virtual recreations of traditional slot machines that can be found in Las Vegas. Various kinds of slot machines exist today, though their overall rules and mechanics are pretty much all the same. The primary goal of any slot game out there would be to line up different symbols in different combinations within the pay line of the machine. Depending on certain combination odds, however, these games can payout quarters or even millions in dollars. The amount that a slot will actually pay out mainly depends on which kind of slot machine you play on, though. Therefore, before you try to learn how to play slots, you need to understand the different kinds of online slot machines out there.
Most slot machines out there have two pay lines and three reels. Basically, every pay line has three reels that represent only one bet. Reel and pay line amount variations are probably where the biggest differences in slot machines lie (the differences in appearance aside that do not impact the game rules whatsoever anyway). Also, depending on the amount of symbols and reels that the slot machine has, the overall payout table will differ, as well.