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Slot Machine Technology
Random number generator
It is a common belief
that the odds on a machine have something to do with the number of each
kind of symbol on each reel, but in modern slot machines this is no longer
the case. Modern slot machines are computerized, so that the odds are
whatever they are programmed to be. In modern slot machines, the reels and
lever are present for historical and entertainment reasons only. The
positions the reels will come to rest on are chosen by a Random Number
Generator (RNG) contained in the machine's software. This is called
"virtual reel" technology.
The RNG is constantly
generating random numbers, at a rate of thousands to millions per second.
As soon as the lever is pulled or the "Play" button is pressed,
the most recent random number is used to determine the result. This means
that the result varies depending on exactly when the game is played. A
fraction of a second earlier or later, and the result would be different.
Payout percentage
Slot machines are
typically programmed to pay out as winnings between 82 to 98 percent of
the money that is wagered by players. This is known as the
"theoretical payout percentage". The minimum theoretical payout
percentage varies among jurisdictions and is typically established by law
or regulation. For example, the minimum payout percentage in Nevada is 75
percent and in New Jersey is 83 percent. The winning patterns on slot
machines, the amounts they pay, and the frequency at which they appear are
carefully selected to yield a certain percentage of the cost of play to
the "house" (the operator of the slot machine), while returning
the rest to the player during play. Suppose that a certain slot machine
costs $1 per spin. It can be calculated that over a sufficiently long
period, such as 1,000,000 spins, that the machine will return an average
of $950,000 to its players, who have inserted $1,000,000 during that time.
In this (simplified) example, the slot machine is said to pay out 95%. The
operator keeps the remaining $50,000. Within some EGM-development
organizations this concept is referred to simply as "par".
"Par" also manifests itself to gamblers as promotional
techiniques: "Our 'Loose Slots' have a 93% Pay-back! Play now!"
As an aside, the "Loose Slots" actually may describe an
anonymous machine in a particular bank of EGMS.
A slot machine's
theoretical payout percentage is set at the factory when the software is
written. Changing the payout percentages after a slot machine has been
placed on the gaming floor requires a physical swap of the software, which
is usually stored on an EPROM but may be downloaded to Non-Volatile Random
Access Memory (NVRAM) or even stored on CD-ROM or DVD depending on the
technological capabilities of the machine and the regulations of the
jurisdiction. Based on current technology, this is a time consuming
process and as such is done infrequently. In certain jurisdictions, such
as New Jersey, the EPROM is sealed with a tamper-evident seal and can only
be changed in the presence of Gaming Control Board officials. Other
jurisdictions, including Nevada, randomly audit slot machines to ensure
that they contain only approved software.
In many markets where
central monitoring and control systems are used to link machines for
auditing and security purposes, usually in wide area networks of multiple
venues and thousands of machines, player return must usually be changed
from a central computer rather than at each individual machine. A range of
percentages are preprogrammed into the game software and selected by
configuring the machine remotely.)
In 2006, the Nevada
Gaming Commission began working with Las Vegas casinos on technology that
would allow the casino's slot manager to change the game, the odds, and
the payouts remotely via a computer. The change cannot be done
instantaneously, but only after the selected machine has been idle for at
least four minutes. After the change is made, the machine must be locked
to new players for four minutes and display an on-screen message informing
potential players that a change is being made.
Linked machines
Often machines are
linked together in a way that allows a group of machines to offer a
particularly large prize, or "jackpot". Each slot machine in the
group contributes a small amount to this progressive jackpot, which is
awarded to a player who gets (for example) a royal flush on a video poker
machine, or a specific combination of symbols on a regular or 9 line slot
machine. The amount paid for the progressive jackpot is usually far higher
than any single slot machine could pay on its own.
In some cases multiple
machines are linked across multiple casinos. In these cases, the machines
may be owned by the machine maker who is responsible for paying the
jackpot. The casinos lease the machines rather than owning them outright.
Megabucks may be the best known example of this type of machine. Megabucks
Nevada starts at $10,000,000 after a jackpot. (Prior to September 2005,
Megabucks Nevada reset to $7,000,000.) The new penny Megabucks video game
also has a jackpot that starts at $10,000,000.
Slot machines that are
not linked to a large regional jackpot such as Megabucks usually have
higher payout percentages, as linked machines have to take into
consideration the large jackpot amount into their payout percentage
calculations.
Near-miss programming
Because the reel display
of modern slot machines is controlled by computer software, it is possible
to make the slot machine frequently display combinations that are close to
winning combinations. For instance, if the jackpot combination is
"7-7-7", a slot machine could be programmed to frequently
display "7-7-(non-7)". This can fool the player into thinking
they "almost won", teasing them into playing more often.
This practice of showing
combinations that are similar to winning combinations more frequently than
would occur randomly is called "near-miss" programming. It has
been ruled illegal in the U.S. states of Nevada and New Jersey. The Nevada
Gaming Commission did review some machines with this type of programming
and refused to authorize them.
There is a related
phenomenon that is also sometimes called "near-miss". The chance
of a winning combination appearing on a payline is controlled by the
winning percentages programmed into the slot machine. However, the
combinations appearing above and below the payline are all roughly equally
randomly distributed. This means it is much more likely that a
"winning combination" will appear above or below a payline than
on the payline. Using the same example above, it is much more likely that
a "winning combination" of "7-7-7" would appear on a
line above or below the payline than the chance that it would appear on
the payline.
The issue of a near-miss
above or below the payline was also investigated by the Nevada Gaming
Commission. They ruled that this was legal, so long as the
"near-miss" above or below the payline was not specially
programmed. In other words, the "near-miss" must be just as
likely to occur as any other combination. The machine cannot be specially
programmed to show "winning combinations" more frequently than
other combinations above or below the payline.
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