The Modern Slot Machine - Overview of RNGs

The Modern Slot Machine

Slot machines are the most profitable gambling activity for the gambling operator.  In fact, slots routinely generate more than half of all casino profit.  That’s the reason they are the first thing you see when you walk into a casino, and the last thing you see when you walk out.  That’s also one reason they’re the loudest, brightest, and most prevalent form of gambling.  Because of this, we need to spend a little extra time fundamentally understanding how modern slot machines function.

In this lesson, we’ll take a behind-the-scenes look at what happens when you pull the lever in a modern slot machine.  We think you may be surprised by what’s really happening!

Common Misconceptions of Slot Machines

This may be shocking, but there are many stories from casino employees who report patrons wearing adult diapers or even in some cases peeing on the casino floor (gross!) instead of getting up from the slot machine from fear of someone else hitting the jackpot on “their” machine once they’ve left.

Unfortunately for those patrons (and the poor person who has to clean up after them) they fundamentally don’t understand how slot machines work.  Think you do?

Let’s test your own knowledge of slot machines with a couple true or false questions:

Question 1

You’ve just hit 9 consecutive losing spins in a row.  On your 10th spin, you are now more likely to hit a winning spin?

Question 2

You’ve spent the last hour playing a slot machine. You really have to pee, so you get up to use the bathroom.  When you come back to “your” machine, you see someone else is playing it, and to your horror, they hit a big jackpot!  Had you stayed at that machine and kept playing, that jackpot would have been yours!

What is a Random Number Generator (RNG)?

RNG stands for “Random Number Generator”.  This is the core technology of modern slot machines.  Slot machines, whether in physical casinos or online, use a computer program that includes an RNG.  The RNG continuously generates a sequence of random numbers, even when the machine is not in use.  Each number corresponds to a specific outcome or combination of symbols on the slot's virtual reels.

The slot machine's program maps each random number to a specific set of symbols on the reels.  There are far more virtual stops (combinations) than physical stops on the actual spinning reels.  This means that a virtual reel can have hundreds or even thousands of stops while the physical reel may only have around 20-30 symbols.

Slot machines are designed to display the outcome of a spin the moment you press the spin button or pull the lever.  The outcome is determined the millisecond you initiate the spin.  If you had pressed the button a fraction of a second earlier or later, the result would have been different because the RNG would have generated a different number.

The RNG generates numbers at such a rapid rate that it's impossible to predict the sequence or know when a specific outcome will occur.  When you finish playing on a slot machine and someone else sits down to play, the RNG continues generating numbers during that time.  

Moral of the story?

Let's Reflect

How do you think understanding how modern slot machines work could influence your approach to playing them?

How might understanding the technology behind slot machines change your perspective on the gambling industry as a whole?

Closing Thought

Understanding how RNGs work is one of the keys to seeing through smoke and mirrors that make slot machines the most profitable tool for casinos.

For a deeper dive on slot machine design, we highly recommend the book Addiction By Design, by Natash Dow Schull.