Random Number Generators and Slot Machines

Has this ever happened to you: you're playing your favorite slot machine for nearly two hours, hoping to get that big jackpot but never really winning it. You take a break for lunch and come back an hour later just to see someone else playing your machine hit the big one. Is your first thought, "That's my jackpot! If I had only stayed I would have won it all.” Don't believe it. Slot machines are based on a sequence of pseudo-random numbers and, in a way, the timing of your play.

An slot machine is a computer (Electronic Gaming Machine or EGM actually) and computers can't really create random numbers, but can generate sequences of numbers that mimic randomness - Pseudo Random Numbers which are widely known as PRNs.  These PRNs are pretty good:  they're exercised with battery of tests run against the output to ensure the numbers are statistically random.  The most common algorithm, the linear congruent method (LCM) which generates numbers such that same sequence of numbers won't occur until about 2 billion numbers have been generated. Many EGMs use variations of the LCM that have cycle periods close to the number of molecules in our galaxy!  You can't guess the sequence even if you know the algorithm.

As a rule, EGMs generate a random number continuously, not every time you drop in a coin. It's not unusual for EGMs to generate over 1000 numbers in the sequence every second. Only when you place your bet does the machine capture the next 'random' number.  Knowing the algorithm isn't of much help since you'd have to drop your coin into the machine and bet at the exactly right 1/1000th of a second in order to get the number you were counting on.

Once the number is generated, the computer compares the number to a payout chart.  All games have a payout table referred to as the PAR (Percentage Average Return) chart. Each EGM has it's own individual PAR chart, usually ranging from 99% to 81%.

Every game (even if they look the same) has a different PAR chart and the chart is usually held as confidential by the casino. The payout rate advertised on the machine or in the casino usually portrays an average of all the games taken together. Since each game is a separate entity with its own random number generator, it is not uncommon for one game to have a payout of say 95% and the one next to it, with the same game title having a payout of 86%.


To further complicate matters, PAR charts are usually different depending on the amount of the bet.  Maximum bet has the highest return rate while smaller bets typically have a lower payout rate.

Once the payout (or loss) is determined, the slot machine spins the spinners with a command from the computer to land on a certain display.  The spinners really have NOTHING to do with the actual play, it's all handled by a random number generator and a table.  Even the 'bump' of the spinners is pre-determined based on the random number and table.  Sorry to take the fun out of it.

The bottom line is that gaming is truly random. If you are at the right place at the right time with max bet you too could win a sizable jackpot on an electronic gaming machine. The fun part is the anticipation of the win and the many little wins along the way that make slot gaming fun regardless of whether you win or loose.