Generally, they distinguish 3-reel, 5-reel, 7-reel slots, and progressive jackpot slots. The first ones are traditional games; nowadays, they seem outdated due to a little number of paylines. They were replaced by 5-reels. This type occupies a more significant part of the slot sphere; it has more paylines. 7-reels are rare cases. 5-reel games are considered the most popular and fruitful.