The first slot machine was produced in 1895. The person to invent the slots was Charles Fey. Fey worked on the slot machine until 1907 when he sold the first one through Mill Novelty Company. The first slot machine was called ‘Mills Liberty Bell’.
In the first machine you still had the reels we know today. The reels, instead of having bars, had actual playing cards. The king, queen, and jack were on the reels. There was a bell that would ring every time you won the spin. 
During 1910 another slot machine was produced based on the Liberty Bell.
It had a coin entry with the fruit symbols. In fact this slot has several machines mirrored after it such as ‘Fruit Mania’.
It was 30 years later after the first machine was created by Fey that they became very popular. Bugsy Siegel introduced the slot machines into the Flamingo Hilton Hotel in the 40′s which solidified their existence. A lot of the players were female as they would wait for the high rollers to get done playing at the tables. We have seen an increase in North America of the slot machines.
There are two types of slot machines now, you have the progressive slots and the regular slots often called flat tops.
The progressive slots are going to have a jackpot that grows as you play the game. In other words a percentage of what you wager goes to the jackpot.