The random number generator (or RNG) is the heart and brains of all modern electronic casino games

This article explains how the random number generator works. It also tries to clear up some myths and misconceptions.

Read on to learn more about this simple yet complex piece of slot machines, video poker, and keno games in every casino. 


1. Random Number Generator (RNG) defined

A random number generator is a computer algorithm contained on a microchip inside a slot machine or video poker or keno machine. It has the simple function of generating a number between 0 and about 4 billion (4,000,000,000). 

It does this continuously, hundreds of times a second. It functions 24 hours a day, seven days a week as long as there is power.

Because the RNG is programmed it technically is not random. Rather it is a “pseudo-random number generator” (PRNG). This is because the series of numbers must start somewhere and is actually predetermined.

However, due to the sheer volume of numbers generated (about 4 billion, several hundreds of times a second) they mimic true randomness closely enough to be considered random for the purposes of gambling.

As you know, none of the games on the casino floor has approximately four billion possible outcomes. The reels on slot machines have somewhere between 20 and 100 different stops. 

Video poker games have only 52 to 54 cards depending on the number of wild cards.

Keno games have only 80 possible numbers.

To handle these differences, RNGs map the resulting number generated into the proper set of possible positions, or cards, or numbers.

2. How the RNG functions in slot machines

As was mentioned above, the RNG is constantly in motion, cycling numbers between zero and about four billion. 

At the instant the lever is pulled or the spin button is pressed, the current number from the RNG is mapped into the possible positions on the reels and the reels start spinning. They stop at the positions determined by the RNG. 

Some slot machines have a button that will stop the reels. Even when this button is pressed, the reels will stop at the positions determined by the mapping of the number that was generated when the spin button was pressed (or the lever pulled). 

Pressing the stop button will not change the results. It can speed up play, however.



3. How the RNG functions in video poker machines

Like a slot machine, the RNG in a video poker game is constantly cycling through numbers. 

When the player hits the button to deal the cards, the number generated by the RNG at that instant is mapped into the possible cards and those cards are displayed on the screen.

The RNG continues cycling until the player holds the desired cards and hits the “Draw” button. At that instant the number generated by the RNG is mapped into the remaining cards and the results are displayed.

Note: Older video poker machines (several decades older) would map 10 cards on the initial deal – five for the original hand and five replacements should the played not hold some of the originals.

Because enterprising individuals were able to determine the replacement cards based on the original cards on these machines, all current video poker games only map the original five cards and the RNG continues cycling. That minor change eliminated that opportunity to predict the outcome.

4. How the RNG functions in keno games

Like all the other electronic games in a casino, keno machines have an RNG constantly cycling through numbers. This continues until the player has selected the desired numbers and hits the play button.

At that instant the number generated by the RNG is mapped into the count of numbers played out of the 80 possible numbers.

5. Myths and misconceptions

  • While there are winning and losing streaks, they are a function of randomness and nothing a player does will necessarily change that. The play will continue to be random.
  • Hitting the button to stop reels from spinning does not alter the results. Whatever was determined by the RNG will still be the result.
  • If a player leaves a machine and another player sits down and immediately wins a jackpot, that jackpot would not have occurred for the first player. It is virtually impossible to hit the play button at the exact instant required to produce that jackpot.
  • After video poker machines changed from mapping 10 numbers on the initial deal, it is impossible to determine what cards will appear on the draw since the RNG is continuously cycling between the deal and the draw.
Slots Machine


6. Summary 

  • Every gambling machine on a casino floor has an RNG. Slot machines, video poker, video keno, video blackjack, and all other games that require random selection have RNGs.
  • The RNG cycles continuously while power is present.
  • The RNG generates numbers between 0 and about four billion and it does this hundreds of times a second.
  • While an RNG is technically not random (it is pseudo random), it acts close enough to random to be allowed in casino games.
  • There may be winning and losing streaks, due to the functions of the RNG, there is no way to determine when they start or end. There is no way to predict when a game is “due.”
  • Because of the incredible range of numbers and the speed at which they are generated, it is impossible to affect the outcome in any meaningful way.
  • Also due to the range and speed of RNG number generation, if someone else gets a jackpot on a machine a player just left, the original player would not have gotten the jackpot.

Jerry “Stickman” has been involved in casino gambling for nearly 30 years. He is an expert in blackjack, craps, video poker and advantage slot machine play. He started playing blackjack in the late ‘80s, learned several card counting systems and used these skills to become an advantage blackjack player and overall winner of this game. He also acquired the skills necessary to become an overall winner in the game of craps, accomplishing this by a combination of throwing skill and proper betting techniques. Stich is also an overall winner playing video poker.