It will be mere waste of time if we try to categorize slot machines. Since each casino tries to attract players by the wide selection of one arm bandits, there are hundreds of different types and variations - single line, three line, 3 or 5 reel, progressives, bonus games and many others.
All we can do is to list some parameters that can be used while describing a slot machine.
Generally, slot machines have either 3 or 5 reels. The first machines had only three reels and we know them as "regular" or "classic" slot machines.
Nowadays you can easily find slots with five reels. These modern machines usually have more than one payline (see below).
There are one, two or more horizontal rows across vertical reels displayed by the slot machine.
The additional rows, one each above and below the payout window allow players to "see" how close they had come to winning.
A slot machine can have one or more (3, 5, 9 or even 15) pay lines on its reels where symbols must line up on to be a winning combination. Usually it's the center row of symbols across vertical reels.
Classic slot machines have only 1 payline that goes through the middle of each 3 reels. You can wager more than one coin per spin - but the amount will apply to wins on the same payline and your chances of winning will be the same.
If a machine has more than one payline, a player can activate additional ones by increasing his/her bet, but have the option of not playing all available lines.
For example, if you play on a 3 line machine, you should insert one coin to play on the center line, two coins for the center line and the line above it or 3 coins for all 3 lines. So, if you play on the center line with one coin and the winning combination comes up on the bottom line you will not win.
Slot machines with 5 reels can have from 5 to 15 paylines with the diagonal matches.
Slot machines can be found in many denominations from 5 cents to $5. High roller machines can take denominations as high as $500.
Usually it's a three coins machine, but machines with a two coin maximum bet are also available.