How Do Slot Machines Work?

A slot is a dynamic placeholder that either waits for content (a passive slot) or calls out for it using a renderer (an active slot). Slots can be filled with different types of content, but they must have one common element in order to work: They must reference a repository item.

Slot machines have come a long way from the mechanical pull-to-play versions of decades ago. Now, casino floors are alight with towering video screens and glitzy themes. But before you start dropping coins into these eye-catching contraptions, it’s important to understand how they work and what your odds are of winning.


Each machine has a pay line that determines the payout sequence of symbols on the reels. Some pay from left to right, others in zig-zag patterns. All slots have information about the pay lines on their pay tables, which you can access by clicking on the HELP or INFO button.

Random number generator

The random-number generator in a slot machine is a computer program that sets random numbers for each possible combination of symbols on the reels. When it receives a signal — whether it’s the pressing of a button or the pulling of a handle — the computer looks up the sequence of numbers and assigns each to a stop on the reels. Then, the reels spin and, if they’re aligned, that combination of symbols will form a winning payout. The random-number generator also runs continuously, setting dozens of numbers each second.