First slots machines were mechanical devices. The selection principle was an
independent spinning of each reel which were vertically disposed on a common
axis. When a player activated the machine by pulling a lever-like handle, the
reels were caused to revolve freely. Payoffs were based on the horizontal
alignment of symbols after the reels come to rest.
The odds of such machine were determined by the number of reels and symbols
on each reel. The Liberty Bell had three reels each with ten symbols and every
symbol on the reel had an equal probability of showing on the payline. The
chance that a symbol appear on the paying was 1 in 10. So, the odds against
hitting the jackpot on the Liberty Bell were 1,000 to 1, because account for 10
x 10 x 10 = 1,000 possible combinations.
That's how the original slot machines worked.
Today's slot machines are much more sophisticated. They are computer driven,
so everything - the jackpots, sound effects and even the reels themselves - are
controlled by microprocessors, and the main difference from mechanical slots is
that in modern slots, each stop does not have the same probability of showing
on the payline.
Computer chip generates random numbers when you press the "Spin"
button or pull the handle, than the computer uses a mapping technique to
convert the large number into a smaller number or integer that is mapped to the
stops to show you either a winning combination or a losing one.
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