This is what is known about casino slot machines:

The RNG (Random Number Generator)

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The Random Number Generator (RNG) is the brains of the slot machine. While most player know that there is a computer chip picking the numbers, they do not fully understand how it works and this can lead to some of the many myths and misconceptions about a slot machine. One of the most common myths is that a machine has a cycle that can let a player know when it is due to hit. – This is completely false and heres why. Inside the slot machine is a microprocessor similar to the one in your home computer. Instead of running Word or Excel, it runs a special program known as the RNG. This generates numbers to correspond to the symbols on the reel of the slot machine and decides the outcome of the game cycle. You might say that the RNG is in perpetual motion. As long as there is power to the machine it is constantly selecting random numbers every millisecond. The RNG generates a value between 0 and 4 billion (approx number) which is then translated into a specific set of numbers to correspond to the symbols on the reels. The outcome of each spin is determined by the number selected by the RNG. This number is chosen with the 1st hit of the spin button or 1st deposit of a coin. The RNG uses a formula known as an algorithm which is a series of instructions for generating the numbers. The scope of this is beyond most of our mathematical knowledge but can be checked and varified for accuracy. This is done by the Casino Control Board and other testing laboratories to make sure that the program performs as it should so the player will not be cheated. While all of this may sound reasonable it still does not give the normal person any basic understanding about how the RNG works. I would like to try to explain it in a simplified manner that I think most of us can relate to. Although this is not precisely how the RNG operates it should give you a basic understanding of the principles of how the winning spins are determined and how little affect the payout percentage chip installed in a slot machine actually has. Reel type slot machines have a number of spaces and stops on each reel that contain either a symbol or blank. These are refereed to as the physical stops. Most of the old mechanical machines had reels that could hold 20 symbols while the modern slots have reels with 22 physical stops. The micro processing technology allows the newer machines to be able to accommodate a large number of “Virtual stops”. I will try to simplify things by saying this: Imagine that there are only 10 stops on each reel. With 10 stops there can be 1,000 different combinations. We get this number by multiplying the number of symbols on each reel. (10 x 10 x 10 = 1,000) The 1,000 combinations that can be attained are known as a cycle and this is the word that sometimes confuses a player into thinking that the machine has cycles of winning and losing. The odds of a three number combination being picked are one in a thousand. Theoretically if you play 1,000 spins you should see each of these number combinations once. However we all know that this is not the case. If you played a million spins you would see that the numbers would even out to be closer to the actual probability. This is similar to flipping a coin 100 times. Although the odds are 50 -50 you are unlikely to see 50 heads and 50 tails after 100 flips. This is similiar to a Daily pick 3 lottery drawing. They have three glass bowls or drums each containing ten balls numbered 0 -9. The balls are mixed up and when the top is lifted a ball pops up the tube showing you the first number. This is repeated for the second and third number to give you a three digit winning combination. To use this as an example of the operation of the slot machine, we will replace the numbers 0 -9 on the balls with slot symbols. In each bowl, we will have one ball with the jackpot symbol on it. Two balls with a Bar, three balls with a cherry and four balls which are blank. Imagine the RNG in the slot machine as the person drawing the winning combination. Here is the breakdown of the number of times out of a thousand that the winning combination made.

• 3 Jackpot 1 (1x1x1)
• 3 Bars 8 (2x2x2)
• 3 Cherries 27 (3x3x3)
• Total Wins 37
• There are 963 losing combinations consists of:
• 3 blanks
• 2 blanks and a symbol.
• 1 blank and two different symbols.
• 3 mixed symbols.

The RNG picks these combinations of numbers thousands of times each second. Now imagine a string of blinking lights where only one bulb can be lit at a time. The electrical current is zipping from bulb to bulb down the string. When you push a button the current stops moving and the bulb in that position lights up. In this example the light represents the three digit number just picked by the RNG. If you hesitated a second before pushing the button the results would be different. This is the same as you getting up from a machine and seeing someone else sit down and hit the jackpot. The chances are astronomical that you would have hit the spin button at the exact same millisecond.

All this comes down to this:

The percentage chip payout is based over the life of the machine. The expected service of any Commercial slot machine is at least 40 million game cycles. It might pay back 500% today and 10% tomorrow. It could also pay 180% for a month straight and then 2% for a year. The average will equal the percentage chip installed in the main board. This is why when you are at a casino you can dump $1000 or more in a slot machine, take a 5 minute walk to the restroom and when you return to the machine you were playing you see someone else sitting there with a smile from ear to ear because they just won a jackpot that should belong to you, after all the money thats in the machine was yours, wasn’t it?

Slot Terms and what they mean

• PAR = Paytable and Reelstrip listing though it is widely refered to as the pay out percentage.
• HFRQ = Hit Frequency.
• PSR = A program summary report

From what I have learned, there are two factors that are figured into a slot machine to eventually come up with the PAR. One of those is the hit frequency and the other is the win frequency. They are mutually exclusive, Example: – If you have a high hit frequency, you will have a low win frequency, and if you have a high win frequency, you will have a low hit frequency. Hit frequency is how often the machine actually pays something, and win frequnecy is how often a big jackpot is paid. All of this shapes how volatile the machine is. The way I understand it is you can’t change those factors and not mess with the PAR, and that is part of what GLI checks with the math.

If you know what you are looking for, you can actually observe it during machine play. Compare the play on a Double Red White and Blue with a Triple Red White and Blue. While the theme sounds the same, the volatility of the machines are worlds apart. You should see lots of small payouts on the double RWB and few jackpots,and the opposite on the Triple RWB.

Hit frequency depends on how many of the possible combinations result in a win. If there are 262,144 possible combinations (a three reel, 64 positions per reel game). We may have, say 61,700 possible winning combinations (taken from a real game). For the example given, on the average about 23% of the games will result in a win of some kind.

The hold of the game may be altered by either changing the number of winning combinations, or changing how much gets paid on a certain win. The first can be done without a change in the Pay Table. The second will reflect as a change in the pay Table.

All reel games I have ever seen have many possible combinations to give a different Hold. The intention is that a different denomination for a given game be set to a given Hold. A casino can choose to have 2.5% of a dollar, or 10% of a quarter, and so on, each giving the casino about the same revenue per coin played.

Hit frequency varies more according to different games than within a given game. A higher hit frequency makes a game more exciting The pay awards are usually lower, but coming more often. A lower hit frequency game usually has higher payouts, but is hit less often. Both games can have the same Hold.

Hit frequency depends on how many of the possible combinations result in a win. If there are 262,144 possible combinations (a three reel, 64 positions per reel game). We may have, say 61,700 possible winning combinations (taken from a real game)”

So I gather that “positions” mean symbols on the reel and Is that a typical amount of combinations? (64 ^3)

My Experience with hands on debugging of many micoporcessors and some limited programming. It seems to me with todays video processing power it could be a huge number of positions and combinations. ( I mean the reels don’t actually spin any more, its more just scrolling video data. The same goes for the RNG (Random Number Generator). To put it in layman terms, how many positions/possible combinations would a “money to burn”, “winning bid”, “jackpot party”, etc have?

Well, Generally there are aproximately 32 positions per reel. (Ok 5 reels = a really big number.

High jackpot value = really low hit rate on the Jackpot, but lots of small wins.

Most of the hardware is pretty standard microprocessor circuits with only a few bells and whistles added. De-engineering is seldom difficult if you have done it before. Dis-assembling firmware is time consuming but an excellent learning experience. You really get a good understanding of how the game works.

Most Stepper (reel) games have only 22 reel stops including the blanks. However, virtual numbers are assigned to the reel stops. which means that the reels can be weighted. As an example assign more virtual numbers to the blank spaces on a slot machine reel. (usually blank spaces around the symbols for the top award) This of course intices players to stay at a machine for longer periods. Im not totally sure but with the memory limitations on IGT S+ machines highest number of virtual reel stops is 64^3 however on video reel machines appear to have as many as 88 reel stops (no virtual stops for video since they are virtual reels) now the strange thing is that they can have more reel stops for some reels than others. eg:

A game with 5 reels can have 60 stops for the 5th reel 70 for the 4th 72 for the 2nd and 3rd and 88 for the 1st this would yeild 1,916,006,400 reel combos. thats a whole lot to work with. you could imagine the possibilities in tweaking either the PAR or HFRQ by fractions of a %. – All This is just my opinion, of course!

A slot machine simply takes a dollar and gives 80-98 cents back (it's rare to find a slot machine with a payback of over 98%).

But, of course, it does this in the long run.

Since playing slot machines seems insane on paper, what makes slot players spend so much money on these machines that are often referred to as one-armed bandits?

That'll be all the psychological factors.

Slot Machines and Psychology

A machine that just takes money and does nothing else would unlikely succeed, so the way slot machines have worked around that hurdle is offering a theoretical chance to win money, even if you lose money on the machine in the long run.

And that chance makes people play the machines. First of all, who wouldn't want to win a lot of money for basically doing nothing? That's appealing even if the odds were against you.

Additionally, people rarely realize just how much of a house edge slot machines have, and how much better it would be to play games like blackjack with optimal strategy.

Usually, the bigger the jackpot, the more players are willing to play the machine. After all, what's $50 spent on a machine that may give you a life-changing sum of money? (Co-incidentally, progressive jackpot slots, the ones that have more than a million dollars in jackpot prizes, give you the worst winning odds.)

Our desire to win big-time allows slot machines to play another psychological trick on us: the near-miss situations, which happen because slot machine reels are weighted differently (more about that lower on this page). It encourages us to keep on playing since we 'came so close' to winning life-changing money.

At live casinos, the most popular slot machines are often placed in the places where most people can see them. This takes an advantage of a psychological tendency called Social Proof (or as I like to call it, 'monkey see, monkey do'). Some say that casinos even place the machines with the highest hit frequency to where everyone can see them - I find this believable, but I have no proof.

Seeing lots of others play and win is one heck of a psychological trick. The sound of winning that a slot machine makes is affiliated deep in our mind with something positive, as is the sound of coins clinging and clanging against the metal disposer of the machine (the sound of money!). It's easy to see why someone walking in to space like that would be hooked.

So I thought it would be important to understand how slot machines work from a psychological point-of-view first - since psychological factors are what make us play slot machines - and now that you understand the basics of slot machine psychology, let's move on to the technical aspects.

Random Numbers and Paytables

When someone believes in a slot machine's hot and cold streaks, it's called Gambler's Fallacy, and for a good reason. 'Hot' streaks happen, 'cold' streaks happen in the sense that sometimes, when numbers are chosen randomly, they happen to be of similar sort for X times in a row.

It's like receiving pocket aces twice in a row at poker - it's unlikely (in fact, there's a X% chance it happens) but it does happen sometimes. Does that mean the deck of cards is 'hot'? Or when you flip a coin and you get heads five times in a row, is the coin 'hot'?

Of course not. When things happen at random, they do. They're unpredictable. Anything can happen, and at some point probably will happen.

But the point is, you have no way of knowing what the future holds for a slot machine. Every spin of the reels is an independent trial, which means the previous game has no influence on the next game. Everything starts over and the chances of winning are the same with each spin of the reels, regardless of whether someone's lost ten spins in a row or just hit a jackpot.

Why would anyone design slot machines that get 'hot' or 'cold' anyway? If they did, players could tell when to play and when not to play. It makes no sense. Casinos are much better off creating slot machines to which there are no 'winning systems' available.

So slot machines use a random number generator (from now on referred to as 'RNG') to, well, generate random numbers for each reel. These numbers are between one and a couple of billions (let's just say a lot of numbers).

And there's a symbol assigned to each number - for example, if the RNG would pick numbers between one and a billion, the game had ten symbols and each were as likely to come, there would be a 100 million numbers assigned to each of the symbols.

Slot Machine Eprom Chip

But lot machine symbols are never equally likely to come; the ones that pay the most are the hardest to get. Therefore different symbols have a different amount of numbers assigned to them. (The odds of winning the Megabucks jackpot are somewhere in the one out of 50,000,000.)

But the point is, the RNG assigns numbers to each reel and those numbers correspond with symbols that have been assigned to them. The RNG is not influenced by previous results; it deals a new, random set of numbers with every spin, regardless of what's happened.

Interestingly, the moment you press Spin or pull the lever, your fate has already been sealed. Spinning reels stopping one by one is just theatrics; they make the game more exciting and enjoyable.

Slot Machine Chips

Now, the slot machine must also know which symbol combinations are winners and how much they pay. For this, slot machines use EPROM chips. They tell the slot machine winning combinations and define the paytable.

When a casino wants to change the payback of a machine, they change the EPROM chip (or the settings of the chip). Not long ago casinos had to physically change the chip which was quite a bit of work, but now many casinos can change the settings of the chip externally.

There are rules, though. In Nevada, for example, casinos aren't allowed to change the settings four minutes before and after someone has played; this eliminates the myth that casinos change the settings while you're playing.

So either someone physically changes the chip or there has to be a four minute time window before and after someone's played. (While the settings are being changed, the slot machine screen should have a message stating that some sort of 'configuration' is happening.)

That's pretty much it. There are a lot of psychologal tricks involved, but technically the RNG assigns random numbers to each reel and the EPROM chip determines the winning combinations and paytables, which together determine the payback (or 'return') of the machine. The less it pays back, the more you're going to lose on the machine in the long run.

More About the Subject:

• Vegas Click: Michael Bluejay's comprehensive explanation of how slot machines work. In my opinion, the best one out there.
• Wizard of Odds: Michael Shackleford's slot machine advice -- the site also features an extensive FAQ section for slots.
• Gambling Captain: If you're looking for a short but insightful read on the basics of slots (or other casino games), this is a good site to visit.