Ask the Slot Expert: Does each denomination on a slot machine have its own RNG?

Question: I heard just recently that Multiple Denomination machines have a separate Random Access Generator for each different Denomination chosen. Is there any truth to this?

I always thought there was only one per machine no matter if it was Multi-Denomination or not. Say if it's a 97% or 85% return machine it is the same no matter what Denomination I chose, or go back and forth between.

Answer: Slot manufacturers are notoriously reluctant to discuss details about the Random Number Generator functions in their machines. If you search online for "rng cheat slot machine" you'll get many hits for people who have been able to use knowledge of the RNG function in slot machines to cheat the machines.

Your question implies that there might be something different about the RNGs that accounts for the change in return on the two denominations. The RNG has nothing to do with how much a machine pays back.

Let's say we have two egg cartons that each contain 12 ping pong balls. Each carton has a mix of white and gold balls. In one carton, the mix is 50/50. The white balls are in the even-numbered slots and the gold balls in the odd. In the other, the mix is 75% gold and 25% white. Slots 1 through 9 are gold and 10 through 12 are white.

We also have a random number generator black box. Whenever we press the button on it, it shows a new number, from 1 to 12, chosen randomly on its display.

We're going to use the black box to choose ping pong balls at random from the cartons and keep a tally of how many of each color were chosen from each carton.

We hit the button. It's a 7. We add 1 to the gold ball tally for carton 1 and 1 to the gold ball tally for carton 2.

We hit the button again. The number is 11. We add 1 to the gold ball tally for carton 1 and 1 to the white ball tally for carton 2.

We do this many thousands of times. We have a lot of free time now because most scripted TV shows aren't going to return for a few more weeks.

We check our tallies when we are done. For carton 1, the ratio of gold balls drawn to total draws is very close to 0.5, as is the ratio of white balls drawn to total draws. For carton 2, the ratios are close to 0.75 for gold and 0.25 for white.

Same RNG function. Different results.

The RNG just generates a stream of numbers that satisfy many of the tests for randomness. It's up to the program running the slot machine to do something useful with those numbers. Slot machines return less for lower denominations of the same game by changing the layout of the symbols on the reels. Video poker returns less for lower denominations by paying less for certain hands.

I did some searching online to see what others are saying about the RNG. I found this post from three years ago written by a "retired senior software engineer with years of software development experience for a gaming company."

There is one and only one pseudo random number generator in all slot machines. It is a software algorithm that runs at blazingly fast speeds, generating thousands upon thousands of pseudo random numbers every second. There are only two pseudo random number generators authenticated and permitted under the regulations of the Nevada Gaming License Control Board (GLCB). The pseudo random number generators cannot be altered, nor can they be “tuned” to alter game outcome.

I don't know when he retired. He warns that his experience is in Nevada and he "retired a few years ago, so it is possible (although unlikely) that things have changed."

On May 24, 2012, Nevada's Gaming Control Board issued a Notice to Licensees, one section of which deals with Regulation 14.040(2), which deals with the RNG. This document says:

Games that offer RNGs for purposes other than determination of game outcome (e.g., Keno Quick Pick) must use a separate RNG than that used as part of the game random selection process.

In this example, the machine has two RNGs. Perhaps the poster meant that there is only one RNG used for game outcome determination.

The first chapter in The Art of Intrusion by Kevin Mitnick is "Hacking the Casinos for a Million Bucks." Here is an excerpt from the section in which the hackers hack into the RNG code on an American-made video poker machine.

[They] discovered that the random number generation process was much more complex: The machine used two generators operating in combination, instead of just one.

The programmers of this machine made a mistake that made it easier to hack. The proper way is to get a new random number from each RNG and combine the two values someway to determine which card will be dealt next. The mistake these programmers made was to get a new value from one of the RNGs only at the beginning of a hand, so it remained constant through the hand.

That's another instance of a machine with two RNGs. Game programmers, however, may only know that they call a certain function to get a random number and may not know everything that happens in the process of generating that number.

I've played some Asian-themed slot machines on which the paylines go from double digits to five when you switch from a cent-based denomination to a dollar-based denomination. These machines probably load a new game program when you make that denomination change. In that sense, you could say that there is a different RNG for the two denomination classes.

But machines don't have multiple RNG functions running and call the penny one when the denomination is a penny, and the 2-cent one when the denomination is 2 cents, and the nickel one when the denomination is nickels, and so on.

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