Credit meter

A credit meter keeps track of how much credit the player currently has as well as winnings when the reels are spun.

Credits are often used instead of showing actual cash amounts because, to the player, losing credits may not seem as negative as losing money.

Arm or button

Once the player has selected how many lines they want to bet, pulling the arm or pressing the bet button locks the settings, selects a random number, and spins the reels.

Bet button

When the bet button is pressed, the number generated by the RNG at that exact moment is selected and used.

Reels

Reels are for show, and by the time they’re spinning the machine already knows what the outcome will be. Spinning and stopping reels in sequence helps build suspense and excitement for the player, keeping them more interested.

Stops

Each reel usually includes 20 to 30 stops, which are the symbols and blank spaces on the reel.

Single-reel example

Required legal payout percentage

Many states have laws that require certain payout percentages. For example, a machine that returns 85 or 90% of the cash it receives over time would still give the casino a 10% - 15% cut.

Weighting

The programmable EPROM allows weighting to fine-tune the play experience.

For example, if a reel has 10 blank spots, as long as that quota is met, it doesn't matter which blank spots are used. The machine could be programmed to land on blank spots around jackpots to give the player the impression of a "near win."

Stacking the odds:
multi-reel machines

On a multi-reel machine, the odds of winning decrease exponentially. For example, taking the single reel example from above and multiplying it to 3 reels (all with identical symbols as the first), the chances of a winning combination (3 of the jackpot symbol instead of 1) drop from 1/20 chance to 1/8000 chance.

Anti-tamper

Slot machines are designed to be tamper proof to both the players and the casino.

Cabinet & screen

The cabinet and screen act as a faraday cage to disperse electricity and ground electrical signals, preventing outside electrical signals from interfering with the machine’s processes. The screen is coated in a clear, electrically conductive chemical, and connects to the metal cabinet to allow conductivity between the two.

Coin comparator

The coin comparator accepts or rejects coins that are put into the machine. It compares incoming coins against a coin previously placed in the comparator (e.g. if a nickel is in the comparator, then the machine would only accept nickels).

EPROM

The EPROM is programmed and tested in factory, then placed in the machine with a tamper evident sticker over it. This style of chip is reprogrammable using ultraviolet light and must be removed from the machine to do so, which is allowed only when a gaming authority is present.

Reels

Reels have sensors that detect extra movement, so trying to move reels manually causes an error to display on the LCD screen and any winnings are negated.