Progressive slot machines have been around for a very long time in the offline casino world, but there are many reasons as to why they have reached their full level of prominence only after being converted into online slot machines. One reason for this is the fact that you can now play free slots with attached progressive jackpots and while you do not get a chance to win the progressive jackpot from the free slots version, you can at least get a taste for how things work. This has led many people to convert from free slots to paid slots once they have had a taste of the progressive jackpot and that in turn has resulted in much more popularity for progressive slot machines as a whole in the online arena.
Progressive slot machines are varied in how the machine actually works. Some of the slot machines will be conventional in nature while others will be video slot machines. What defines a progressive slot machine is therefore not exactly what type of slot machine it is, but rather the fact that it has a jackpot attached to it that increases with the steady passage of time if nobody wins the slot machine grand prize. In this sense, progressive slot machines can be any type of slot machine so long as this jackpot is present and in the case of all progressive slot machines, the progressive jackpot replaces the normal top prize that another slot machine of the same basic type would have.
One of the things to keep in mind about progressive slot machines is that because of this increased progressive jackpot, the odds of the slot machine keep changing. The effective pot odds (to use a poker term) of the progressive slot machine gets larger as the jackpot gets higher and for that reason there are rare circumstances in which the progressive jackpot gets so large that you can actually turn the odds to your favour by playing the slot machine at that particular time. It is a rare occurrence however, but by the time the jackpot gets to that size the casino has already made so much money off the slot machine that it does not mind giving a little back.