First slots machines were mechanical devices and the odds of such machine were determined by the number of reels and symbols on each reel. The selection principle was an independent spinning of each reel.
The Liberty Bell had three reels each with ten symbols and every symbol on the reel had an equal probability of showing on the payline. The chance that a symbol appear on the paying was 1 in 10. So the odds against hitting the jackpot on the Liberty Bell were 1,000 to 1, because account for 10 x 10 x 10 = 1,000 possible combinations.
In the new computer controlled slot machines this is not the case as the reels have no independent action. They are being perfectly coordinated by the RNG and the computer. It is clearly explained by Henry Tamburin in the article Slot Machine Myths.
Nowadays a slot machine returns between 85 and 100 percent, depending on the game and location and the average house advantage is calculated to be about nine percent. It means, that in the long run the particular machine will give back 91 cents for every dollar played. It keeps nine cents on the dollar.
Of course, people would not play slots if every time they put a dollar in they got 91 cents back. Instead, a slot machine is programmed to return percentages explosively and this volatility is what makes slot playing fun.
You will hardly find other casino game with such an enormous built-in edge against you. Nevertheless, slots are so popular today that they now constitute 70 percent of all casino action.
Of course, the house edge reduces your chances of winning the jackpot as compared to mechanical slots. On the other side, if you hit the jackpot in the modern slots it will be much larger then the original ten nickels of Liberty Bell.