Classic slots have three reels and a single pay line. They are the easiest slot machines out there and players usually have to match the right symbols in order to win. Side games tend to exist for this kind of machine, including symbols with small bonus prizes, and wild cards that look like random symbols for better chances.
When it comes to classic slots, there are higher chances of prizes getting higher, depending on bigger bet amounts, because winning capacities increase the way the lottery does.
Several slot machines exist that run like the lottery.
As every turn gets played and its big jackpot remains not won, the jackpot keeps getting higher until someone matches the three symbols correctly. This way, the big prize accumulates, making the combination more difficult to match, even though the entire program remains built on RNGs. To make the jackpot higher, it would be smart to play high money amounts because the payout is going to end up much bigger because it will depend on how much money gets played.
Once the jackpot gets won, the prize is going to rest back to the first prize and increase from there. On a lot of machines, this process happens on automated screens, even though, sometimes, it seems that a limit has to be reached prior to a winner coming out from it.