1. Casino Slot Machines How Do They Work
2. Casino Slot Machines How They Work
3. How Casino Slot Machines Work

Introduction to How Slot Machines Work

In these series of posts, I continue to answer the most common questions about slot machines asked via Google searches. This post explains the simple question of how slot machines work.

Most modern slot machines are designed to look and feel like the old mechanical models, but they work on a completely different principle. The outcome of each pull is actually controlled by a central computer inside the machine, not by the motion of the reels. The computer uses step motors to turn each reel and stop it at the predetermined point. While the first thing that pops into most players’ minds when they think of a classic slot machine is a three reel machine, there are also five and even seven reel classic slot machines. They can have one, three, or five rows and can either use mechanical old time reels or video screens that display the reels. Traditional slot machines are programmed in such a way that it accurately registers the total wager of a player and rewards a player based on his or her total wager no matter how big or small his.

In this post, I will discuss the operational components of a slot machine from the point-of-view of a slots player. Meaning, the various interface areas on the front of a slot machine. These player interface areas include:

• Service Light
• Bonus Display (Optional)
• Pay Table
• Players Club
• Results
• Play Console
• Ticket In, Ticket Out (TITO)

Additional relatively minor interface areas are not listed or shown below. These areas are the locations audio speakers, audio volume control (optional), display lights, lever arm, and a hearing aid jack to accommodate those with a hearing disability.

Keep Reading … or Listen Instead!

Subscribe to my Professor Slots podcast at Apple Podcasts Google Podcasts Spotify Amazon Music Amazon Audible Gaana Stitcher Pandora iHeart Radio Tune-In SoundCloud RadioPublic Deezer RSS and everywhere else you find your podcasts!

Service Light

A slot machine’s service light is generally located at the very top of a slot machine to be easily visible to casino employees. Because of this uppermost location, it’s also known as the candle within slots terminology.

Slots players can switch on the service light by activating the service button on the player console. Or, it will enable by itself if the player wins a hand pay jackpot or the slot machine develops a service fault. Faults might include lack of paper, a full cash-in condition, mechanical or electronic tampering, or an internal electronic failure such as CPU overheating, etc.

Modern casinos have a slot attendant call/dispatcher communication system using a headset and microphone. This setup is helpful for spotting problems on the casino floor. An activated service light automatically notifies the casino operating system. The casino dispatcher then informs the slot attendant responsible for that section of the casino.

Casino Slot Machines How Do They Work

Once the notification is sent out, a lit candle is of little practical use. At best, it guides the responding slot attendant the last few feet to the customer needing attention and, also, provides some reassurance to the waiting customer.

Slots players may activate the candle for a multitude of reasons. In general, they do so to deliberately call a slot attendant to their location, for any of a host of reasons only limited by imagination.

Pro-Tip #1: Service Light

Sometimes slots players need to leave a slot machine briefly but don’t want to give it up to someone else. If this break is relatively brief, say 10-15 minutes, use the service button to call over a slot attendant. The slot attendant can temporarily lock up the slot machine at the request of the player.

Casino Slot Machines How They Work

The slot machine can be unlocked later by the player via insertion of only their service card … or after 10-15 minutes when the temporary lockout automatically expires. For the specific length of lockout times, ask any slot attendant at your casino.

Bonus Display Area

If a specific slot machine has a bonus round available, then it will often have a second display area. Video slots may use the same primary display screen but abruptly display the bonus round game theme instead. However, video slots most often have a secondary display screen available for bonus rounds.

The Bonus Display area is optional and dependent upon the specific slot machine model. The location of this bonus display varies. More often than not, it is high up on the slot machine to be viewable by other players from a distance.

Casinos offset their losses by offering slot machines with bonus round display visible from a distance. Frankly, wins on these highly visible and usually loud bonus displays are seen by many. This obvious win encourages other casino patrons to play slot machines.

Pro-Tip #2: Bonus Round

Bonus rounds generally cannot be activated unless that slot machine’s maximum credits are bet. By not betting maximum credits, the player automatically lowers their odds of winning.

If betting maximum credits on a specific denomination slot machine is not affordable, pick another affordable slot machine. I discuss this approach in detail at Choosing Slot Machines.

Pay Table Area

The Pay Table area lists information on the jackpot amounts for specific reel combinations. It can also display some or all of the game theme rules. This area may be permanently displayed on the slot machine, or possibly only available through an interactive series of images available by touchscreen.

In either case, all possible wins may or may not be displayed. Sometimes the list is highly abbreviated, and displays only the highest jackpots, due to space limitations. Other times, mainly with touchscreen displays, a series of images can be switched between to view every possible winning combination.

However, pay tables typically provide the highest value jackpot. Slot machine game themes with multipliers or “wild” reel symbols have their most top value jackpots being the result of these reel symbols. Alternatively, it may not show all multipliers or “wild” symbols in the tabulated list of win-reel combinations. Instead, they may be in writing along the edge of the paytable interface area.

But, with large touchscreens has come the capability to provide full paytable information along with game theme rules. Some slot machines now have this feature and, perhaps, more will have it in the future.

Many paytables show the number of credits that would be won for a specific combination of reel symbols. Or, they may show a monetary amount. In either case, these tables have separate columns for winning combinations dependent upon how many credits are bet. The far–right column typically shows the winning jackpots available when betting maximum credits.

Some examples of credit and denomination combinations are:

• 1-credit slot machines having a $100 denomination
• 3-credit slot machines having a $5 denomination
• 5-credit “quarter slots” having a $0.25 denomination
• 300-credit “penny slots” have a $0.01 denomination

Pro-Tip #3: Pay Tables

Frankly, learning the paytable of any slot machines played is a relatively easy way to improve the odds of winning at slots. Many typical slots players believe there is no skill involved in winning at slot machines. Casinos gently foster this misunderstanding, as it is to their benefit. Don’t fall for it.

Traditionally, slots players find it acceptable to play slot machines with visual succinct paytables. Frankly, casinos would instead have their customers spend their time playing a game they don’t understand.

The casino isn’t making money if a player spends time studying or reading until they do understand rather than playing the machine.

One easy-to-learn skill to improve the odds of winning at slots is choosing which slots to play based on their paytables. I discuss this in detail at Choosing Slot Machines.

Players Club Area

The Players Club area contains a card reader, numbered keypad, and a small display. A security feature of players club cards is for players to choose a PIN to enter when they wish to access their player account.

Newer-style slot machines have a touchscreen display, which removes the need for a physical keypad. Meaning, it’s part of the touchscreen display.

Bets can be made on a slot machine without a players’ club card. At most casinos, it typically is not required. Neither is the PIN needed to play the device or view basic information. For example, a running total of reward points earned during the current play session is generally on display.

The PIN is required, however, to:

• access certain portions of player’s casino account
• transfer banked funds
• activate “free play” provided by the casino as a complimentary gift

Results Area

The Results interface area is where the reel combinations are seen after making a bet. Whether a video slot machine or a slot machine with physical reel, this is where the results of a bet are provided.

Interpreting whether a reel combination is a winner requires an understanding of the paytable. This result is fundamental to how slot machines work.

Of course, the slot machine will immediately display the results. A small display beneath the reels shows:

• the total amount of money or credits available in the machine
• how many credits most recently bet
• the jackpot amount won if any

Jackpots are usually in credits, where each credit equals the denomination of the machine rather than the amount bet, as well as a monetary amount.

Player Console

How Casino Slot Machines Work

The Play Console typically has physical buttons, a cash/ticket reader, and a ticket printer. The buttons include:

• Cash Out for requesting the removal of any player funds in the machine
• Service to request a casino attendant
• A Series of Buttons for selecting the number of credits to bet, or placing the maximum possible bet
• Cash Out for removing any remaining bankroll
• Repeat to making another bet for the same credit(s)
• Denomination to select a specific bet denomination (optional)

The player console may have several possible button configurations, dependent upon the model of the slot machine. Given how often game themes are switched to maintain the interest of players over time, it is common for player consoles to be standardized over many machines within a casino.

Also, it is becoming common for consoles to have embedded displays visible through their semi-transparent button covers. This array of small screens are linked together to show visually stunning composite images displayed across the entire array of buttons.

Ticket In, Ticket Out (TITO)

By the beginning of the 21st Century, the use of coins was removed from casinos. This removal was for the sake of convenience of both the casino and customers. Both had issues with handling so many coins. Customers because of the difficulties inherent with carrying so much weight, but also gambling delays due to full (or empty) slot machine coin hoppers.

Casinos had issues with coins as well, including customer complaints due to delays caused by a full (or empty) slot machine coin hopper. This inconvenience was a coin logistics issue, which also included higher costs of maintaining a larger vault space and coin processing equipment and services. As casinos became more popular, coins became more difficult for everyone.

As a result, Ticket-In, Ticket-Out technology was pulled into casinos. They are now integral to how slot machines work. This automation is the same technology that was beginning to be seen in Automated Teller Machines (ATMs). Once proven out, this slot machine technology was here to stay like so many others.

Summary of How Slot Machines Work

I’ve discussed the operational components of a slot machine from the point-of-view of a slots player. This explanation of how slot machines work included the various player interface areas on the front of a typical slot machine.

There are additional relatively minor interface areas. These areas include audio speakers, audio volume control (optional), display lights, lever arm, and a hearing aid jack to accommodate those with a hearing disability.

Related Articles from Professor Slots

Other Articles from Professor Slots

• Previous: Where Were Slot Machines Invented Historically?
• Next: Why Do Slot Machines Say Bar on Their Reels?

Have fun, be safe, and make good choices!
By Jon H. Friedl, Jr. Ph.D., President
Jon Friedl, LLC

No other segment of the gaming industry has benefited more from the technology revolution than the slot machine. Once considered the ugly stepdaughter placed on the gaming floor to appease the spouses of table players, the slot machine has been transformed into the fairy princess of the gaming world. With her, she has brought a dowry of riches no one would have imagined for the casino and a few lucky players as well. Over twenty years ago the slot machine accounted for 30 percent of the casinos' profits. Today it accounts for about 70 percent. Computer technology and the ability to play with little to no gambling knowledge makes it possible to offer life-changing jackpots big enough to turn a pauper into a king.

However, the fact that it doesn't take much gambling knowledge to play means that most people don't understand the inner working of the slots -- which makes it easy to explain a loss or a win with some false logic. Like any other 'wives tales' these are passed from person to person until they become gospel. Most of these myths and misconceptions are harmless but they can add to your frustration and take away some of the enjoyment of your casino visit. Let’s take a look at a few of the most popular myths and the truth behind them.

Myth #1

Someone hit a jackpot on the machine you just left -- so you would have won that jackpot if you kept playing.
This is probably one of the most common notions about slot machine gambling -- but it's patently false. The slot machines have a computer chip inside that runs the Random Number Generator (RNG). The RNG is continuously cycling through numbers even when the machine is not being played. These numbers correspond to the stops on the wheel that display the winning or losing symbols that you see when the reels stop. When you hit the spin button or pull the handle, the RNG picks the combination at that given microsecond. If you had stayed at the machine, it is highly unlikely that you would have stopped the RNG at the exact nano-second to display that same combination of numbers. In the time it takes to talk with a friend or sip your drink the RNG has cycled through thousands of combinations.

Myth #2

You can tell the odds of winning by counting the symbols on each wheel.
Actually, you can't. The RNG generates a number for each spin. There can be hundreds of virtual stops on each wheel even though you only see a few symbols. For example, you may see 20 symbols on each wheel of a three-reel machine. You figure 20 x 20 x 20 = 8,000 combinations and your chance of hitting the jackpot is 1 in 8000. In reality, the computer chip may program 256 stops for each wheel which makes the odds 256 x 256 x 256 =16,777,216 combinations. Being able to generate millions of combinations is the reason that slots can offer large paybacks.

Myth #3

Casinos can loosen or tighten the slot machines with the flip of a switch.
In actuality, the slot machines have a computer chip in them that determines the payback percentage. These are preset at the factory. In order for a casino to change the payback, they would have to change the chip. In most jurisdictions, there is paperwork that has to be filled and submitted to the Casino Control Commission for each machine if the chip is changed. It's time-consuming and the chips are very expensive. For this reason, it is more economical to decide on the payback percentages before purchasing the machines and having the factory ship them with the proper chip.

Myth #4

A machine that has not been paying out is due to hit.
There is no way to determine if a machine is due to hit. Each spin is a random occurrence and has no bearing on what has happened previously. Don't ever play more than you should because of this misconception -- it will be devastating to your bankroll if you do.

Myth #5

The temperature of the coins played will affect the way a machine pays.
Unfortunately, the machine is not affected by temperature. It doesn't matter if you play hot, cold, old or new coins. The coin slot is a mechanical device and has no feeling.

Myth #6

If you use your slot club card the machine will pay back less.
This may well be the most damaging myth of them all. There is no link between the card reader and the RNG, but by not using your player's card you are denying yourself valuable comps and sometimes cash back from the casino.