Slot machines can be broken down into all kinds of categories — casino slots and online slots; flash and downloadable; free and real money; single-line and multi-line, etc. But casino slots can fall into another two primary categories (that online slots cannot): reel/mechanical slots and video slots. Since video slots also have reels (albeit virtual reels), the preferred term is mechanical slots. Mechanical slots are the forerunners of video slots.

There are obviously no mechanical slots in online casinos and there are fewer and fewer mechanical slots in land-based casinos, as well. Nonetheless, mechanical slots are the grandma of all slot machines and, as such, they deserve a few words (and a major tip of the hat). After all, slot machine history begins with the mechanical slots.

Mechanical slots are comprised of physical wheels — usually three but sometimes five — called reels. Printed on these reels are symbols; on mechanical slots there are usually classic symbols like fruit and bells as opposed to cooler, theme-related symbols on video slot machines. When a player inserts money into the slot of a mechanical slot machine and pulls the lever, the reels spin around and the symbols arrange themselves in a horizontal line (called a payline). The machine's pay schedule will determine whether the combination that has formed will turn you into a winner (or not). Usually, on a mechanical slot, the player needs three identical symbols in a row to win.

Video slot machines work in a way very similar to mechanical slots but they are run by computers. Their reels are simulations of reels and there are way more possible combinations in a video slot than in a mechanical slot. Many video slot machines are way more complex than a mechanical slot machine can possibly be (with tens of paylines), but there are also many video/online slots that hark back to the days of the basic mechanical slot machine and have one payline and 3 reels.

These machines also use classic symbols like bars and the number 7. For many people, making the transition to an online casino is one thing; leaving behind the traditional slot is another.

Though some video slots are made to look like mechanical slots, the guts of the two types of machines are totally different. The outcome of a mechanical slot is directly related to the pull of the lever and to the number of times a symbol appears on a specific reel. The video slot, on the other hand, is fueled by a computer, specifically by a Random Number Generator, which spits out thousands of possible stops every second. Mechanical slots are the classic slots we all still imagine when we picture a casino slot machine; they are the famous "one-armed bandits." But video slots have taken over and, with them the sky's the limit in terms of jackpots, lines, combinations and themes. Video slots have brought us into the 21st century but we can never forget that it all started with the classic mechanical slot.