In earlier days, people used to believe that the probability of winning on the slot games machines is somewhere related to the count of symbols of each type on the reels. But the idea does not exist anymore.

Virtual Technology

In the slot machines of modern times, the probability of any symbol turning up on the machine is programmed in software. The knob and reels are supposed to be present only for the purpose of fun since they have been present since the olden times. The symbol that will land up on the reel after pulling the knob is decided by a random number that will be generated in the software of the machine. This is known as Technology of Virtual Reels.

A random number is continuously generated by a generator which would vary between thousands and millions of numbers in a second.

Whenever the player pulls the knob or presses the Play button, the random number that is generated recently determines the symbol landing up on the machine. So, the outcome is all dependent on the player's timing to pull the knob. A second before or after will change the outcome.

Proportion of Payouts

Normally, the percentage of payout would vary between 82% and 98% of the amount that is gambled by the player. This percentage of payout is known to be theoretical. The minimum percentage of this theoretical payout is generally governed by jurisdiction and set according to laws. For instance, this factor is set to 75% in Nevada whereas it is 83% in New Jersey.

The percentage of the bet amount that goes to the machine operator is selected based on three factors namely pattern of winning on the machine, winning amount and the rate of their occurrence. For instance, consider a slot machine that has a cost of 1 dollar for every spin. After some time, say after 1 million spins, the total cost that would have been invested would be 1 million dollars. A machine paying at a percentage of 95% would pay back 950,000 dollars to the players while keeping 50,000 dollars for the operator. This logic is simply referred as "Par"by some of the organizations. This technique is mostly used for promoting among the gamblers.

The percentage of the theoretical payout of the slot machine is set at the time of coding the software. It is not so easy to change these percentages after placing the slot machine in casino as it requires physical swapping and change in the software. The software is generally loaded on EPROM but can be downloaded to NVRAM (Non Volatile RAM) or can even be copied to DVD or CD ROM which would basically depend on the machine's technical capabilities and the laws set by the jurisdiction. Physical swapping of software will consume time as the present technology used in the machines is not so efficient. As per New Jersey jurisdictions, there is a seal on EPROM and so changing it requires the presence of officials from Gaming Control Board. Jurisdictions at other places would hardly check the authenticity of the software.

Software Auditing

Many a times, these slot machines are connected together to form a WAN (Wide Area Network) mainly for the purpose of security and auditing. In such cases, the percentage of bet amount that goes to the player is governed by the central system. These percentages are coded into the software in the form of a range which can be selected by remote machine configuration.

In Nevada in 2006, a gaming commission started working on this technology to change the payouts, the game and the chances of winning via remote connection to a computer. It was put to use in casinos in Las Vegas. But it was only possible to implement the change on a machine after it has been free for more than 4 minutes. After implementing the change on the machine, it is assigned to a new player for a minimum of 4 minutes and informs the players of the change in the form of a message on the screen.