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Are Slots Really Random? - The "true" RNG


By: “Vegas Vic” – Victor H Royer

I have been writing a column on casino games, and slots, for the past 32 years, in continuous publication nationally, and Internationally. Over these many years, I have received hudreds of letters from readers from all over the world. And, over these same many years, it seems that the Number 1 question I am always asked is: “Are Slots truly random?”  Shortly followed by something like this: “What is the RNG? Is there really any such thing?”

The general context of the correspondence usually goes something like this:

“I was playing this machine, and I hit a jackpot, and then it died. How come the machines always seem to “know” that it paid out a jackpot, and now all of a sudden it stops paying? If this was really a random game, then it shouldn’t just “die” like this. Are these machines somehow “set” so that they have to “make up” the money they paid out before paying out again?”

There are several variations on this theme, and this question, but all generally center on this same subject. I have written about it before in many of my columns and books, and so have other writers and gaming columnists.

So, what gives? How come we all keep being asked this same question over and over again?

I guess the answer is that we are all so close to the subject, that we probably feel like everyone should know this. But there are many people who still don’t read books and articles on casino games and gambling on a regular basis (which they should), and many other people who just never heard of this RNG thing before. And, of course, there are new players, and younger players, who have all come into casinos over the past 30+ years, and not all of them have read our stuff (sadly, but they should – self plug). And so it is that this is a question that seems to puzzle just about everyone, and very often.

In my book: “Powerful Profits from Sots”, Chapter 10 – and also in my books on “Casino Secrets” – I provide the full and complete analysis of what exactly is the RNG (Random Number Generator), what it does, how it works, and how and why slots are really and truly as random as humna programmers can make them. Or any computer, for that matter.

To spread the word, so to speak, about the “true and real randomness of slots”, here in this article I am going to provide an extract from that chapter, and my other writings, where I will explore – and hopefully explain and answer – that perrennial age-old question: “Are slots really random?” At the end of this article I will also share some updates, and other thoughts, such as what is really happening with AI (Artificial Intelligence), and what is also happening with the Meta-Game concept in slots programming.

So, here is the true story of the RNG:

The reason for this article is to tell you about the RNG – the Random Number Generator – a computer program that runs all modern slot machines, regardless of whether they are video or reel. I have been asked many, many questions about this, and therefore it seems appropriate to revisit this subject yet again, and make it clear – or, at least as clear as possible. There are more details about this in my books on Slots, Video Slots, Video Poker, Keno, and Casino Secrets. You can find all of them through my web site: www.MoreCasinoDeals.com 

Gaming literature, particularly books and articles on slot machines, are full of references to the RNG – the Random Number Generator. This is often described as the program which randomly selects the winning combinations, running constantly until it is triggered by the deposit of the first coin, or credit played. However, no one has thus far actually told us what it really is, and how it really works. At least not to my knowledge. In reality, there is no such thing as “The RNG”.

What there is, is a computer program, part of which is what is usually described as a Binary Numerical Sequencing Algorithm. What this means is a series of sequenced numbers in binary code, which form the basis for an illusionary program, offering a sampling randomization. In effect since nothing can be programmed to be truly random, this method of acquiring random sequences produces the illusion of randomness, to a mathematical model and formula which can be sufficiently quantified to produce the desired verifiable results, and thus allow for the slot machine to pass regulatory testing and compliance standards.



While I was researching material for my books on Slots and Video Poker, I wanted to offer something more about slot and VP machines than is normally found in books and articles on slots. I thought it would be interesting to find out what the RNG really is, and how it really works. In fact, is there really anything such as that? The conclusion I reached is this: There is a program that can be called the “RNG”, which is part of another program, which is part of yet another program, and these programs, working together, is what allows the modern computerized slot machine to function in the manner in which it does.

However, this program is really not a true RNG, as it is commonly understood. Therefore, the moniker “RNG” is really just a way of expressing what the reality actually is.

To understand what I mean, I offer you the following extract from a series of conversations I had with my friend Dan. “Dan” is not his real name. The content of what follows is not all that there is – just all that is possible to include in this article, to offer a glimpse into the real workings of the slot machine, for the purpose of letting you know exactly how, and why, it works, and works the may it does.

Here then is the reall truth of how the slot machine programs work, and how and why they are as “random” as a human programmer can make them. In the words of my friend Dan, and as written and partially paraphrased by myself:

“Slot machines are controlled by programs, and these programs are stored on a computer chip, called an EPROM (Erasable Programmable Read Only Memory). The chip is in a sealed location on the printed wire board, and changing it, or taking it out, is not a trivial matter. A lot of paper work has to be filled out, and there is quite a procedure to follow in order to take the slot off-line, change out the chip (perhaps change the belly glass), and then put the slot back on line. The EPROM contains, among other things, the Virtual Reel Table. Though the player sees the Actual Reels – spinning behind the glass or simulated on a video display – these reels are only a display to show the player what had already been determined several seconds earlier.

In a lot of cases, the Actual Reels will contain 11 symbols and 11 spaces, for a total of 22 positions. On a 3-reel machine, that means that there would be 22 to the 3rd power – (22^3) – the number of possible combinations, in this case 10,648. If there was only one jackpot symbol on each reel, then some players might imagine that the odds of hitting all three jackpot symbols would be one in 10,648. They are dead wrong!  Actually, the odds of hitting the jackpot, or any winning combination for that matter, are not determined by the Actual Reels, or the number of symbols and spaces on those reels.

The real odds of hitting the winning combinations, are determined by the Virtual Reel Table. This information is never made available to the player.

Every slot comes from the factory with a specific Virtual Reel Table, and a specific Pay Table. The player can see the Pay Table, but they can never see the Virtual Reel Table. There is also another document that comes with every slot machine, and that’s called a Par Sheet. This Par Sheet tells the casino the exact odds for every winning combination on the slot machine in question, and also tells them what the “long-term” Payout Percentage is for that particular machine. There are also some other pieces of information on the Par sheet – one of those is the Hit Frequency. Hit frequency has to do with how often something will be paid back to the player. I have a lot of this information in my books on Video Poker, and Casino Secrets.

The Virtual Reel Table, in combination with the Pay Table, determine the actual “long-term” Payout Percentage for any given slot. The Virtual Reel Table is usually populated with many more symbols and blanks (ghosts), than what the player sees on the Actual Reels. For instance, it is not uncommon for the Virtual Reel Table to contain 63 or even 127 different virtual stops. For 63, that would allow 250,047 possible combinations and 127 would allow 2,048,383. Obviously, this makes it possible for machines with only 22 symbols on the Actual Reels, to offer a Jackpot prize of much greater than only 10,000 coins – or credits.

It is tough to write a good RNG. We all know that in actuality a better term would be Pseudo-RNG, since anything that is programmed is not truly random. However, there are ways to make a pseudo-RNG look to a slot player like a true RNG. It is also a reasonable opinion, that all RNG routines are written to produce a very basic random distribution of numbers. Once this is done, it is up to the Virtual Reel Table and the Pay Table to account for the actual Payout Percentage.

G.L.I. (Gaming Labs International), is one of the largest slot machine testing agencies in the world. When a slot machine is submitted to them for testing, the randomness of the output must pass a stringent Chi-Square test – and if it doesn’t, the slot cannot be sold to the Casinos. Here is basically how the slot programmers accomplish the task of creating a “perfect” distribution of numbers.

Say we wanted to have a routine that would give us a “perfect” distribution of numbers from 0 to 9.  To be completely random, and completely fair, we would want to see each number the same number of times. In other words, if we ran this generator 100 times, we would expect to see 10 zeros, 10 ones, 10 twos, etc., etc. Now, one way this could be accomplished would be to simply start with a “seed” of 0 and then add one to it each time. Of course the numbers would be coming out in order, rather than in a random order.

 Well, there is a software routine that is a well known algorithm, that will accomplish just exactly what we want done. It’s called a Linear Feedback Shift Register (LFSR ). It’s a little complicated to explain here, but, basically, it is a register of bits, and each time a clock pulse clocks the register, a bit falls out one end of the register, and it is “exclusive-ORed” with one of the middle bits, and is fed back into the start of the register. It’s easier to see this routine in action than it is to try and explain it. If we had a 4-bit register, there would be 15 non-zero combinations that this register could produce. Obviously, an LFSR will not work with all zeros loaded into it for a seed. However, any one of the 15 possible non-zero combinations can be loaded into it, and then if clocked, it will produce exactly one instance of all the 15 possible combinations, and then start all over again. What’s even nicer is that it will produce these combinations in a random order, rather than a sequential order.



In a real slot machine, the LFSRs contain a lot more than just 4 bits. It is more than likely that they would contain 32 bits. With 32 bits, there are a lot of possible combinations. In fact, the total number of possible combinations is 2^32, or 4,294,967,296 total combinations. Say the LFSR is clocked at a rate of 1,000 times a second – again, not an unreasonable number. In this case, we can see that for the LFSR to generate just one full cycle of combinations, it would take 1,193 hours, or approximately 49 days. That’s assuming the power is on 24 hours a day – if it is, the LFSR is running through combinations whether or not anyone is playing the slot.

So, when a player puts in a coin, or pulls the handle, or presses the Spin Reels Button – it really doesn’t matter what the trigger is – the program goes out to the LFSR and gets the next 3 bit patterns that happen to be being generated at that instant in time. Of course these 32 bit patterns equate to decimal numbers that are 0 to 4,294,967,296.  If you recall, the Virtual Reel Table only contains 63 positions on each reel. Therefore, these raw numbers must be divided by 63, and then everything is thrown away except for the “remainder”. This process is known as “modulo” arithmetic, and will result in numbers from 0 to 62. The program then takes these three numbers and looks them up in the Virtual Reel Table, in order to determine which symbol on the Actual Reels to display. If it is a winning combination, it will queue the Credit Meter to credit the player with the appropriate number of coins.

There is one other thing – since 4,294,967,296 is being divided by 63, that means that essentially each of the 63 positions is really mapped to 68,174,084 combinations from the LFSR, and since there are 1,000 numbers per second being generated, we actually can see the entire range of 63 numbers occur about 16 times a second.  Therefore, we aren’t waiting for 50 days to have the possibility of seeing the entire range of 63 numbers occur for any one of the reels. This is how I understand these things to work, and this is how it must be in order to pass the tests at G.L.I.”

So now you know what a slot machine really is, how it works, and why it is really random.

In its reality, it has nothing to do with the pretty pictures you see on the reels. It has nothing to do with the number of stops on the actual reels you see, or the number of spaces on them. It all runs from the virtual reel table, in accordance with the programs as outlined in this article. It’s simply, and purely, a matter of numbers. The results of the combinations are merely numbers themselves. The pictures you see on the reels are merely the graphics which are made possible by the graphic interface, on video reels, and by the command to display just that combination on the traditional-looking reel machines.

To be able to make a machine which holds as close as possible to these “randomness” standards, the manufacturers sends the Par Sheets to the testing labs. These Par Sheets contain, among other things, the following information:

1       Long-term Payout Percentage

2       Probability of Each Winning Combination

3       Odds of Each Winning Combination

4       Pay Table

5       Win Frequency

6       Hit Rate

7       Date of Manufacture

8       Serial Number

By manipulating the values, the Payout can be adjusted up and down. This then allows for the availability of different payback percentages, and therefore, different pay tables, and house “hold”, on games which are, or appear, as the same, or identical. That’s why one casino can have the game set at a payback of, say, 92%, while another casino can have exactly the same game set at the payback of 86%. The adjusted sheet then reveals the contents of the Virtual Reel Table for any given Payout Percentage.

And that’s the true story of the RNG, and how slots really work.


Modern Slots Update

In modern slots, there are some newer variations on this process. They are called AI, for “Artrificial Intelligence”, and “Meta-Game”, for a new set of “randomizations”. But slot machines cannot be truly AI. If that was the case, then the slot machine would “learn” from its “experiences”, and then adjust itself accordingly. That would be highly illegal. While this concept may some day be employed in skill-based casino slots, that day is not yet here. So, some of the most sophisticated newest slot machine programs use instead what can be described as a “Defined Universe Artificial Intelligence” programming. This means that the “total” size of “all possible outcomnes” is fixed, just like the number of possible “bits” in the LFSR example (as shown earlier in this article).

This then in turn means that whatever the “brain” of the slot machine can “think of” – or “determine” – as the next combination to be displayed (winning or losing), can only be “sourced” – or obtianed – by the slot machine’s program from that closed and defined universe. So, the outcome is that the machine still cannot “learn” anything, and that satisfies the regulatory requirements for a random and “non-thinking” slot machine.

To help the computer program “randomize” its results, in a manner more “unpredictible” than the “bits” generated by the LFSR, another program is used, one that can be best described as the “Meta-Game” variation. You may have heard a lot about “meta game” when used in conjunction with sports, such as: “The team used a meta game concept to outwit the defence”, or in general conversation, politics, science, and so forth.

In simple terms, “meta” means “over”, or “outside”, or “something extra”. In the Dictionary, the word “Meta” is described, in part, as: “pertaining to or occupying two positions”. So, when speaking about “Meta Game”, what this means is that we are thinking in two parts, occupying, so to say, two differentiated aspects of thinking about the same thing. Sometimes this can be colloquially described as “thinking outside of the box.”

But in modern slot machine programming, especially those that use sophisticated randomization protocols and the defined AI universe concept, “Meta-Game” means a second randomizing program that sorts of “thinks outside of the box”, and thus “scrambles” the randomness of the already randomized selections created by the initial and original program.

So, what exactly does all of this mean to you? Other than a headache?

Well, in playing modern slots, those that may be using this new programming (and most still do not), this means that the “selection” of “events”, whether winning or losing, is now even more random, because – to put it simply – the computers now “scrambles” the results more than once before the final choice is made. This has the effect of eliminating the “clumping of bits”, which could theoretically be the otcome of the LFSR, although, mathematically, the final results of selections still came to the same end-percentage. But the more “modern” whay of doing this has the direct effect of assuring a more mathematically-correct representation of randomness, and thus this makes the slots perform in fewer “hot” and fewer “cold” streaks. In a nutshell, the slots are now even more “really random” as they ever were.

And that, my friends, is – for the time being – the latest about the randomization of slots, and how and why slots truly and really are, always as perfectly random as they can be made by human beings under the restrictions of the various regulatory jurisdictions, within which your favorite casino operates.