For the better part of the last century, slot machines were simple enough. They consisted of a metal box that housed spinning, mechanical reels with symbols on each reel. If the symbols lined up and matched, then the player won a jackpot.

Over the last three decades, computer and video game technology have caused big changes in how slot machines are played. Gamblers still see spinning reels, but the mechanism is now powered by a microcomputer called a random number generator.

Additional features have become commonplace, and dozens of different types of slot machines have become available. This page lists and categorizes the major types of slot machines available in casinos throughout the world.

Bonus Slots

One of the most common types of slots games now available are bonus slots, which offer bonus games when certain symbols or combinations of symbols appear on the payline. One of the most popular examples of this type of game is the ubiquitous Wheel of Fortune slot machine game, which features a replica of the wheel from the eponymous game show above the machine. When you hit certain symbols, you get to spin the wheel and get a bonus payout.

Banking Games

A banking game is a game in which coins are accumulated until they’re won. Piggy Bankin’ is one of the most popular examples of this kind of game, which has been around for a long time. Banking games should not be confused with progressive slots, which are covered later on this page.

Multiple Reels and Paylines

Early slot machines featured three reels and a single payline, but modern slot machines have a lot more possibilities. Why is this? Computers.

Three reel slot machines often now have multiple paylines, and five reel slot machines have an even greater number of paylines.

These changes have increased the potential size of the jackpots available on these games. It’s not hard to understand the math of why this is possible. If you have three reels with ten symbols on each, the hardest combination to hit has a 1 in 1000 chance of hitting. Any jackpot larger than 1000 to 1 would result in a loss for the casino.

Compare that with a five reel game with 256 different symbols on each reel. This kind of machine would be impossibly large if the reels were actual metal strips, but computers use imaginary reels, with results determined by a random number generator inside. With these kinds of odds, astronomical jackpot amounts can be offered, and the machine will remain profitable.

The number of paylines has increased dramatically, too. Early slot machines had a single payline, but now, common slot machine games offer the following numbers of paylines:

  • 2
  • 3
  • 5
  • 9
  • 20
  • 25

A new type of Australian slot machine game does away with paylines altogether, and these games offer 243 different ways to win. Basically, any combination of winning symbols from left to right results in payouts. These games are hugely popular, and even though the concept sounds a little confusing, it actually become intuitive very quickly during gameplay. In fact, 243 ways slots are wicked addictive fun.

Types of Progressive Slots – Standalone, Local, and Wide Area

Progressive slot machines offer constantly growing jackpots. These jackpots begin with a seed amount from the casino or network, and as each player plays, a tiny percentage of her bet is added to the progressive jackpot.

These jackpost can become astronomically high. The odds of actually winning such a jackpot are also astronomical. These types of games are comparable to the lottery.

Multiple versions of progressive slots are available. For example, a standalone progressive jackpot has a jackpot that’s tied to an individual machine. These types of progressive jackpots are generally in the $1000s of dollars range, and only play from that specific game count toward the progressive. In fact, standalone progressives are similar to banking slot machines.

Local progressive jackpots, on the other hand, feature linked jackpots within a single casino. These jackpots can grow larger faster because every bet on every machine in the network counts toward the growing jackpot. It’s not uncommon for these jackpots to reach into the $10,000s and even the $100,000s at larger casinos.

But the big jackpots are the wide area progressive games. These games link together slot machines from multiple casinos, and their jackpots are life-changing. These are the jackpots which get into the millions of dollars.

The most popular wide area progressive network in the world is called Megabucks, which was launched in 1986 by IGT, the largest and most successful slot machine manufacturer in the world.

Types of Online Slots

All of the above types of slot machines are available in online versions as well as traditional brick and mortar casinos. In fact, in jurisdictions where online gambling is legal but regulated, you can find exact duplicates of the games available at Vegas casinos.

Most of these games are made available via Wagerworks, which was purchased by IGT in 2005 for $90 million. Examples of these branded and popular slots games now available online include:

  • American Idol
  • Dolly Parton
  • Elvis
  • Family Guy
  • Jeopardy
  • Judge Judy
  • Lobstermania
  • Star Trek
  • Wheel of Fortune

Other online slot machine games are exclusively available online. Examples of these include games from Realtime Gaming and Microgaming, the latter of which offers some of the largest progressive jackpots on the Internet.