Understanding the Random Number Generator (RNG)

The RNG Program

Slot machine with reels spinning
"Slot Machine" (CC BY-SA 2.0) by Jeff Kubina

The Random Number Generator (RNG) is the brains of the slot machine. While most players 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. Many “Snake Oil Salesmen” will try to sell you a system for doing just that.

Save your money it can’t be done.

The RNG Program

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, the RNG, that generates numbers to correspond to the symbols on the reel of the slot machine.

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 when you hit the spin button or deposit 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 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.

Principles of the Random Number Generator

Here is a more simplified explanation that's easier to 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.

Reel Type Slot Machines

Reel type slot machines have a number of spaces on each reel that contain a symbol or blank. These are referred 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 new machines to be able to accommodate a large number of “Virtual stops” which I will explain in a future article.

For this example, let’s simplify things and 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 spins.

The Daily Pick 3 Lottery

Many of you have seen the 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.

  • Jackpot 1 (1x1x1)
  • 3 Bars 8 (2x2x2)
  • 3 Cherries 27 (3x3x3)
  • Total Wins 37

The 963 losing combinations consist 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.