Reels

Originally a mechanical wheel with painted symbols arranged periodically along their outer rim, used for randomizing symbols on a slot machine.

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When a spinning reel came to rest, it would display one symbol per reel on the slot machine's pay line.

Most early slot machines had three reels. Others have used 4, 5, 7 and 8, and there are many different variations on the slot machine reel concept these days. Of course, with the inclusion of electronics in slot machine designs, slots no longer require mechanical reels like in the early days of slot machines.

Still, it's a custom in slots games for slot machine to display reels, so all slots continue to feature spinning reels -- though these days the reels are now produced by video and not mechanical. Slot machine players initiate the wagering event by spinning the reels. When the reels come to a rest, the outcome of the bet is determined, and the player is either paid off or loses his wager.

These days, random number generators determine whether the player wins the bet. The RNG comes up with a randomly generated number. This number corresponds to certain reel placements, and the slot machine knows whether the number corresponds to a winning combination and how much the prize is for that combination. So the video reels "spin" and come to a rest, giving the illusion of the classic reel component of slot machines. As soon as the reels stop spinning, the slot machine tells the player if he won and credits the prize money to his slot machine tally, displayed on a credit meter.