BACK TO BASICS AGAIN
How modern slots reach their results, and other myth busting
By Frank Legato
As you know, we answer a lot of letters here at Casino Player. Many of them repeat a version of the same question: How do slot machines determine the results of each spin? The answers to many of these questions dispel myths that stubbornly prevail concerning slot machines:
“I was playing and losing, and on the very next spin after I got up, the next player hit. That was my jackpot!”
“I look for the right pattern on the reels that will indicate a win is coming, and I bet accordingly.”
“This machine hasn’t hit in quite some time. It’s due to hit.”
We field a lot of questions in letters that reveal these myths are still out there and are still believed by many players. For that reason, periodically, I like to go back to basics in this space, with an explanation of how slots work, and how the result of each spin is decided. My last “back-to-basics” article was in June 2024, so it’s time to revisit the subject.
Modern slot machines determine results based on a random number generator (RNG). Before the mid-1980s, when most slot machines had mechanical spinning reels, results were based on gravity and timing. Reels would spin for a predetermined length of time and would be stopped through what’s called a stepper motor. Back then, the mathematically inclined could calculate the odds of each result by counting the number of the machine’s “reel stops,” which was the term for the spots where either a symbol or a blank could land on what was usually a single payline.
The odds on those old machines were limited by the number of physical reel stops. The classic three-by-three lineup—three reels, three stops each—had 22 stops. Jackpots on those games were limited to a few hundred dollars, because the odds of the top jackpot landing depended on a finite number of stops.
Since the reel strips were static, the probability of a top jackpot was locked in. The jackpot level had to be low enough for the machine to make money. The only way jackpots could be raised to more enticing levels was by increasing the number of reels or raising the denomination.
Manufacturers employed both of those methods in the 1970s, producing slots in $1 and higher denominations, and increasing the number of reels on some games to five. However, in 1984, a patent was issued for the “virtual reel” system, and that was when slots took off in popularity—thanks to advertised jackpots in the tens of thousands, and, with the introduction of IGT’s Megabucks in 1986, topping $1 million.
The way they were able to accomplish this was through a computer simulation of the physical reels. The key to the system is a virtual duplication of reel stops. Each stop— symbol or blank—is assigned a number in the program. The stops representing higher- paying symbols, including top jackpot symbols, get the fewest assigned numbers in the program. The lower-paying symbols and the blanks get the most numbers in the program.
The RNG, meanwhile, is a software program that continuously cycles through every number in the program in a random sequence, cycling through upward of 1,000 numbers per second. The instant the player presses the “spin” button or pulls the handle (which has the same effect as pushing the button), the program freezes the numbers generated in that instant, and displays the reel spots associated with each number as a result for that spin.
By law, those number combinations must include the slot’s top jackpot, which must be possible to hit, however remotely, on every spin. The programmers have already set the odds you will hit that jackpot by the duplication of numbers related to the reel stops.
This is how all modern slots pick the results, and this fact disproves those myths mentioned earlier:
The player that followed you can’t “steal your jackpot.” Hitting the jackpot results from timing, not a sequence of events. Once you stop playing for even an instant, the next result is different. By the time you got up, and the other player sat down, the RNG has generated thousands of number combinations. It is virtually impossible that the exact same set of numbers will be generated even seconds apart.
Looking for “patterns” on the reels? No. Every reel result is independent of every other, and the physical reels are nothing more than display mechanisms. They are only there to display the number combinations frozen at the start of the spin.
A machine is “due to hit? No, for the same reason: every spin is independent of every spin before and after it. A machine can go through a spell of no one hitting a jackpot for weeks, and it’s possible you can sit down and hit big on the next spin, or it can go another week without hitting. It’s only “due to hit” the next time a player lines up the magic combination of numbers, and no one knows when that will happen.
Of course, many modern games override this natural state of randomness with what’s called a “must-hit-by jackpot.” This is a progressive jackpot that has been programmed to hit before the jackpot level reaches a predetermined level. In this instance, say a progressive jackpot “must hit” by the time it reaches $1,000. Once the level passes a threshold close to that level—say, $950—the jackpot controller selects one machine linked to the prize at random, and awards the prize.
In this case, one of those linked machines is, in fact, due to hit. However, the jackpot controller is a separate computer linked only to the progressive jackpot meter, not to the slot machine’s program. It identifies a threshold area to randomly award the jackpot, the idea of which is to create “jackpot fever,” with players furiously hitting those spin buttons when the time is ripe—and, consequently, generating a spurt of extra income for the casino.
On normally operating slots with no advertised “must-hit-by” prize, progressive or not, it’s impossible to say that a jackpot is “due.”
These are the facts. They’re facts that few players consider in the heat of battle on the slot floor. Many would prefer to think they can anticipate what a slot machine will do next, or that they can summon luck through some ritual, or just by cheering themselves on as they play.
But hey, that’s what makes slot play fun. So, have at it. It’s all part of the game.
