Slot machines were invented by a man named Charles Fey and tate back to when the first slot machine was created in 1895. Further development of his innovation lead to the production of a more perfected version of his slot machine. At this point Fey had teamed up with Mills Novelty Company who in turn manufactured what would later be called that "Mills Liberty Bell" slot. The machine was composed of a cast iron casing.

The strips on the Liberty Belle slot machine had reel's which were comprised of symbols geared at mimicking king, queen and jack symbols. Originally the machine had a bell that would ring when a winning combination came to, this was eventually scrapped. The concept of the ringing bell upon winning was something that was ported over to modern day slot machines. However these days the slots you'll find at the casinos on the new strip in Vegas, etc... do not ring as they are rather annoying and distracting. Rather the light on top will flash in order to summon an attendant to verify the machine's winning combination and that it wasn't compromised and to pay the winner.

All the basic design characteristics which made up the Liberty Bell slot machine are still applied in principle to a standard slot machine you'll find in any land based casinos these days. 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. Although many of the slots you'll find in land based casinos still used mechanical parts the RNG contained within the microprocessor are what dictate the combination of symbols and more importantly where the reel is going to stop.

It was in 1910 that the Mills Novelty Company had developed a new product and released a slot machine which they called the Operator Bell. The Operator Bell machine featured a gooseneck coin entry system and featured symbols such as fruit symbols which will later and even to this day remain a popular and common symbol found in slot machines. At the time over 30,000 Operator Bell slot machines were made.

In 1915 the era of the cast iron slot machine had ended upon the introduction of a less expensive wood cabinet slot machine by the Mills Novelty Company. Early in the 1930s Mills introduced several changes and advancements to their slots that revolutionized the entire gambling industry.