The true answer to this question is innumerable. They can be fairly minimal when it comes to a land-based casino, but in online casinos, they are countless. This is because online casinos are accessible to millions of people around the world and the space for the slots is unending. There are different ways of categorizing slots but in this discussion, we will describe them from the evolution point of view.
These are the basic and simplest slots and were the first to be played at the turn of the 20th Century. These slots had three reels and about 32 different symbols. During those days, they were large in size and occupied a lot of space. These later evolved to the modern slots that have five to seven pay lines per slot. To win, the player has to get identical symbols on the middle horizontal line.
Multi-pay line slots
As the game continued to advance, a new idea evolved especially with the 5-7 reel slots. Now people could win with more than one pay line. Casinos varied the pay lines so as it was no longer necessary to have similar symbols in a line.
These came to replace the land-based casinos as technology advanced. Now people could play a slot as long as they had access to a video. This is when the bonuses and free spins came into existence.
Due to this advent of video games, many casino games now have bonuses and there can be a lot to learn. Click here to get an idea of what kinds of bonuses are available to players.
This is where the prize money grows while many people continue playing. It happens in online casinos where more people can play the same game. Innovation is continuing to grow and today there are even discussions about virtual slots on the horizon.