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Slot Machines Are Programmed, But Not Like You May Think

30 April 1996

By Alan Krigman

You're right if you think slot machines are programmed to do certain things. Wrong if you think those things are even vaguely like deciding it's time for a jackpot, holding back because folks have been winning, or producing some near-misses to coax more cash from a player's fanny pack when the credit meter runs low.

I'll explain.

Modern slot machines are sets of computer "chips" and other electronic circuits. Any mechanical components you see are window dressing; they could easily be eliminated in favor of prepaid cash cards from which bets are debited and winnings credited, and "touch" screens to activate play as well as view results.

The computers in slot machines are pretty much the same as those in washing machines and countless other home, automotive, office, and industrial equipment. "Programming" is what makes one rotate the reels of fortune, a second soap your socks, a third pump your brakes, and so forth. The computer age didn't result from the math the devices could do. The innovation was that one mass-produced piece of general-purpose hardware could be programmed with instructions, called "software," for many different tasks.

So, a slot machine being "programmed" doesn't imply that it's "rigged." Rather, that a computer chip which could have been utilized by Whirlpool to wash woolens or Ford to inject fuel, instead was used by IGT to synthesize a game of chance.

Part of every slot machine program defines game structure. Things like activating motors to turn wheels, firing electron guns to draw pictures on screens, and counting coins to pay winners.

Another program segment implements the laws of probability. Slot machine makers develop their own proprietary software; all, however, incorporate means to generate continuous streams of random numbers -- terms keep coming whether or not a machine is being played, and there's no way to predict what's next.

Computers actually produce "pseudo-random" numbers, using some sort of mathematical rule. Such a rule might be: divide 1901 by 1951. The quotient begins with 0.9743721168 and goes quite far before repeating. This pseudo-random sequence could yield a one-digit series 9-7-4-3-7-2-1-1-6-8, a two-digit series 97-43-72-11-68, a three-digit series 974-372-116, etc. The series is as good as random because the rule, alone, isn't enough to predict the number deciding the next bet; to do so, you'd have to know just when the computer started-up, how it picked its entry point into the series, the rate at which it advances in the sequence, the instant it detects that a round of play is triggered, and more.

The program also contains a table of payouts and displays for each possible random number. As an example, the list in a simplified 10-position system might specify that a $1 bet returns $3 if #1 is "current" when the button is hit, $1.50 if #2 or #3, $1 if #4 through #6, and nothing if #0 or #7 through #9. Since one of the ten possible numbers wins $3, the probability of this payout is one-tenth, or 10 percent. Likewise, two of the ten numbers win $1.50 so the chance of this payout is two-tenths or 20 percent... up to four-tenths or 40 percent chance of no payout.

Here's how a solid citizen would fare with ten bets on a sequence following the "1901 divided by 1951" rule, entered at the decimal point with no jumps to account for timing: 9/win $0, 7/win $0, 4/win $1, 3/win $1.50, 7/win $0, 2/win $1.50, 1/win $3, 1/win $3, 6/win $1, 8/win $0. In went $10, out came $11. After 10 million bets, each number should appear roughly a million times. Combined, players would have put in $10 million and gotten back $3 times 1 million, $1.50 times 2 million, and $1 times 3 million - $9 million in all. The casino earns the other $1 million.

So yes, slot machines are programmed. Not to sidestep fate. To make the internal computers take you to the cleaners with a game of chance rather than with your laundry. Sumner A Ingmark, whose programming is poetic if not practical, put it perceptively:

Programming makes my computer,
Think like me, but much astuter.

Alan Krigman
Alan Krigman was a weekly syndicated newspaper gaming columnist and Editor & Publisher of Winning Ways, a monthly newsletter for casino aficionados. His columns were focused on those interested in gambling probability and statistics. He passed away in October, 2013.