The online slot game has developed in to quite a complex game in comparison to its large and bulky predecessor which allowed for only one coin and one movement of the arm which was built on the side of the machine.

The first slot machine is called the Liberty Bell and was made of cast iron. Originally the machine had a bell that would ring when a winning combination came to, this was eventually scrapped. The entire concept of the ringing bell was that it would ring the moment a player won anything on the machine. The slot machines that are now found in land based casinos as well as online casinos do not sound or ring with such intensity as those of the ones in the past.

The basic design and principal that the Liberty Bell was built on is still used and applied in the slot machines today. The evolution of the slot machine due to the microprocessor have allowed the slot machine to become far more accurate and less likely to cheat as opposed to the mechanical reel machines with several moving parts such as the Liberty Bell.

Until the 1950s, most slot machines were mechanical, but the end of this decade saw the development of electro-mechanical machines. This period was the peak of slot machines popularity with the introduction of machines such as Big Bertha. Big Bertha, and later the Super Big Bertha, were super large machines that cost over 150 000 dollars to produce but were powered by a five horse powered motor. This machine had eight reels with 20 symbols per reel and only offered 80% payback to players.

Generally slot machines accept a maximum of two or three coins but some multiple coin playing machines offer a range of options. In some machines, the number of coins paid out is proportional to the number of coins deposited. Some will not even pay a jackpot if only one coin is deposited. It is often best to play the maximum number of coins in order to increase the chances of winning.

Many machines are also moving away from actually accepting coins and the industry is becoming a cashless zone. When players hit one of the smaller winning combinations they are usually paid out automatically from the machine. The larger jackpots are paid out directly by an authorized casino employee who is informed of the winning by a light above the machine.