Online slots and video slots are game designers’ dreams.

They can offer bonus events and huge jackpots. They can offer eye-catching graphics, Hollywood-level animation, film clubs and sound effects and rip-roaring thrill rides through motion chairs.

And they can offer jackpots big and small, from a few dollars to keep players going to lifestyle-changing prizes in the millions.

If a pre-1980s designer of three-reel slots could see it all, it would be enough to raise a combination of awe and insane jealousy.

Before the invention of the virtual reel by Bally Gaming engineer Inge Telnaes, even offering jackpots large enough to turn players’ heads was an incredible challenge.

That’s because without a system such as the virtual reel, odds on slot games are dependent on the number of symbols or blank spaces on the reels. Complicating the problem is that on games with physical reels, the reels have to be small enough to fit inside the machine casing.

That’s not an issue on modern online and video slots.

What if it takes video reel strips that are 1,000 symbols long to create the desired odds of winning, frequency of jackpots and bonus events? No problem. Just program the reels to be 1,000 symbols long.

The key is that the reels and symbols take up virtual space, but very little physical space.

That’s in stark contrast to the situation faced by those who work with games with physical reels, mainly the three-reel games that dominated the slot space from the time San Francisco mechanic Charles Fey invented the Liberty Bell in 1895 until the rise of video slots in the late 1980s.

If the reels couldn’t fit inside the machine casing along with all the other workings, it was of no use. 

That puts strong limitations on jackpot size.

Imagine a game with 10 symbols on each of three reels, and one payline across the middle of the reels, as is common on three-reel games. One symbol on each reel is the jackpot symbol. Lining up three jackpot symbols brings the big payoff.

The odds of lining up all three are 1 in 10 x 10 x 10, or 1 in 1,000.

That doesn’t mean the house could pay a 1,000-coin jackpot for a winner. A bet of one coin per spin would mean 1,000 coins per 1,000 spins, Out of that total, the jackpot must be paid, smaller winners must be paid, and a percentage has to be held for the house to make a profit.

Under those conditions, a jackpot of 100 coins would be enormous.

One way to increase the odds against hitting the jackpot and make jackpots bigger would be to allow the reels to stop between symbols, and include blanks spaces in the combinations.

With 10 symbols and 10 blank spaces, there are 20 possible stops. If one on each reel is a jackpot symbol, then the chances of hitting the top jackpot are 1 in 20 x 20 x 20, or 1 in 8,000.

Payoffs can be increased, but that’s nowhere near enough to generate the jackpots in the tens of thousands or millions we see today.

The next thing designers can do is to increase the size of the reels and have more symbols and blanks per reel.

If there are 20 symbols and 20 blanks, then odds of lining up three jackpot symbols are 1 in 40 x 40 x 40, or 1 in 64,000.

Now we’re getting somewhere. It’s not hard to envision a pay table where this machine can pay a jackpot in excess of 1,000 coins. Not necessarily $1,000, mind you. If the coins are quarters, 1,000 coins are $250 and if they’re nickels they’re a mere $50.

You can keep increasing the symbols per reel and keep increasing the odds and potential payoffs, but you quickly run into the size problem. The reels can’t be allowed to grow so large they don’t fit.

That’s where Telnaes came in with work he started for Bally in the late 1970s.

His key invention, the virtual reel, was first used by Bally on Series E1000 games in the early 1980s. Patents on the virtual reel were later acquired by International Game Technology, but use debuted at Bally.

Thanks to Telnaes, programmers could map a “virtual reel.” Coupled with a random number generator, that could make a reel behave as if it had more symbols than it really did while still yielding random results.

Imagine a programmer starts with a reel that has 20 symbols and 20 spaces, but wants it to behave as if it has 128 stops. 

He can have an random number generator use a number set from 1 through 128. Then he can map out a virtual reel that tells the machine what symbol or space to display when each random number comes up.

Applying the map can have the machine show the only 7 space on the first reel any time the RNG generates No. 1. Then it can have the machine show the first of two triple bars any time the RNG generates 2 or 3, the second triple bar on 4, 5 or 6, the first double bar on 7, 8, 9 or 10, and so on down the line.

The numbers don’t have to be consecutive. The key is to proportion the map so symbols occur randomly in the desired quantities.

If you have three 128-stop virtual reels, each programmed for one stop for the 7, now chances of lining up all three 7s on the payline are 1 in 128 times 128 times 128, or 1 in 2,097,152 — a 1 in 2 million-plus longshot that makes it possible to pay out a lifestyle-changing jackpot.

Larger number and smaller number sets can be used depending on the desired odds and play experience. 

But most important is that the virtual reel gives three-reel game designers some of the flexibility that grows naturally out of the format for online and video slots.