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Best of John Robison

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Ask the Slot Expert: How many RNGs in a multi-game machine?

12 August 2015

I’m a keno junkie. It seems to me that my favorite Game King keno machine is easier to hit playing nickels. When I use quarters it seems to pay less often. There is only one RNG per machine, right? Or is there one RNG for each denomination?

And another variation on the same theme:

I play Game Kings. Several of the games on one machine have decent odds -- 97-99% payback. Sometimes if one game is cold, I switch to another for a while, and may alternate between several games before my day is over.

How does this affect the RNG? Are they each on separate RNGs or is there one for all the games? Am I hurting myself by doing that during a cold streak?

Technical information about how the RNG is implemented in a slot machine is very hard to come by. The RNG function is each manufacturer's intellectual property and they guard it very closely. RNG cheats have used technical information about how the RNG works to cheat machines in the past. The integrity of the RNG is crucial to the fair operation of the slot machine -- fair to the casino and fair to the player.

In The Art of Intrusion, Kevin Mitnick describes how a group of cheats used knowledge of how the RNG operated to cheat video poker machines. The method of cheating they used led to the change in regulations that video poker machines could not choose all 10 cards that could be used for a hand at the beginning of the game on the deal. The program could choose only the five cards needed for the initial hand. The machine had to continue shuffling the electronic deck and the program could choose the replacement cards only when the draw button was pressed.

The cheats started by cheating a Japanese-made machine. Then they turned their sights onto an American-made machine, but they found it was harder to cheat. The American machine used two random number generators to generate its results. Still, the programmers made a mistake in implementing the dual-RNG system and the cheats were able to crack the American machine too.

Given that the same RNG function can be used for any game (it's up to the game program to decide if number stands for a Double Diamond or an ace of hearts), I think it's likely that the RNG function resides in the slot's operating system. This way, any game program needs only to call a function in the operating system to get a number from the RNG (which is called polling the RNG) and the game program doesn't have to implement or contain the RNG function's code.

The same situation exists for computer programs. A Windows or Apple program doesn't contain the code to display dialog boxes or write to the disk. The operating system handles these tasks. The programs merely call the operating system functions to display dialog boxes and write to the disk.

So, it's possible that there's only one RNG function in the operating system and every game program on the machine uses it. It's also possible that the RNG function could reside in each game program.

The good news about my not being able to give a definitive answer is that it doesn't matter. Your chances of hitting any winning combination or being dealt any five-card hand are the same both ways. You don't hurt yourself if you switch games or denominations while you play.


John Robison

John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots
John Robison
John Robison is an expert on slot machines and how to play them. John is a slot and video poker columnist and has written for many of gaming’s leading publications. He holds a master's degree in computer science from the prestigious Stevens Institute of Technology.

You may hear John give his slot and video poker tips live on The Good Times Show, hosted by Rudi Schiffer and Mike Schiffer, which is broadcast from Memphis on KXIQ 1180AM Friday afternoon from from 2PM to 5PM Central Time. John is on the show from 4:30 to 5. You can listen to archives of the show on the web anytime.

Books by John Robison:

The Slot Expert's Guide to Playing Slots