A slot is a position in a computer that allows a peripheral to be connected, such as a hard drive or a video card. A slot also refers to a particular location on a motherboard where these peripherals are installed, such as an ISA or PCI slot. A slot> element in HTML is used to mark a placeholder in a DOM tree, which can be filled with a custom value.

In addition to engineering acumen, the design of a slot machine requires knowledge of math and psychology. The appearance of a paying symbol on the reels, or in some cases just above the blank space, makes players believe the slot is close to a win. Studies have shown that this illusion can cause gamblers to risk more money than they would if they were aware of the true probability of hitting a symbol.

The modern version of a slot machine uses microprocessors, and a Random Number Generator (RNG) algorithm to select the stops on each reel. The actual physical reels are still there, but they spin only as a courtesy to the player. The RNG generates a series of numbers each millisecond, and the microprocessor assigns a random number to each reel stop. The stops on the physical reel are then arranged accordingly.

The payouts on a slot machine are calculated according to the pay table, which is displayed on the face of the machine or contained within a help menu on video machines. Typically, payout values are multiplied by the number of coins the player puts into the machine.