Slot machines have a relatively short history when compared with the history of gambling in general.  Due to the efforts of their inventor, automobile mechanic Charles Fey, slots first appeared in 1894.  The first slot machine considered the prototype of modern slots was called "The Liberty Bell", and is on display in a Nevada restaurant to this day.  In the 1930's, slots began to infuse the gambling scene in the American West, and by the 40's were in Las Vegas casinos thanks to the efforts of gangster Bugsy Seigel.  Starting in the 90's slot machines began to become more popular than table games, and have since taken over the entire casino gambling industry - accounting for two-thirds of the total revenue earned by casinos worldwide.

Online slot machines are essentially virtual re-creations of the original Las Vegas slot machines.  There are several different types of slots, although their mechanics and rules are practically the same.  The main objective of any slot game is to line up various symbols in various combinations on the slot payline.  Depending on the particular odds of the combination, the game can payout anywhere from quarters to millions of dollars.  And just how much a slot will payout primarily depends on what type of machine it is.  Thus, before explaining the rules of playing slots, an understanding of the different types of online machines is needed.  First, here is a simple component graph of the structure of a slot machine:

Payline 1   Payline 2	Reel 1                Reel 2                Reel 3

This particular slot machine has three reels and two paylines.  In other words, each payline is composed of three reels and represents a single bet.  Variations of the number of paylines and reels lends the largest difference between machines, aside from drastic cosmetic differences, which have no impact on the rules of the game.  And depending on how many reels and symbols the machine has, the payout table will vary.  The payout table will be posted on all online slots, either to one side of the slot screen, or by clicking a separate button that says "Payout Table".

Before going into the categories of slot jackpots, this is a good point to distinguish the difference between reel slots and video slots, both of which can be played straight or progressively. Reel slots always have three reels (as in the picture above) and generally range from one to five paylines (one payline being the most common). Video slots will always have more than one payline (sometimes in excess of forty paylines) and are usually composed of five reels. There is generally a wider range of coins, including smaller coin sizes, for video slots. However, since there are more paylines and a greater coin allotment, the max bets can get very large at video slots.

Online slots can be classified in two categories:  Progressive machines and straight slots:

The only difference between the two is that straight slots will payout predetermined amounts, whereas progressive online slots payout from an ever-growing jackpot.  Straight slots sometimes are available with a single payline and three reels, but will sometimes have five reels or more and paylines ranging anywhere from three to twenty.  Players have the option of betting in various size wagers (usually $0.25, 0.50, 1.00, 2.00 or 5.00) as well as the number of paylines they desire.

Choosing stake amounts for straight slots (single and or multi-payline machines_ is simply done by clicking on the + or - symbols where the wager box is on the playing screen.  Choosing the number of paylines to bet on is simply done by clicking on a button that says "Bet Max" (meaning play all paylines at once) or by clicking the "Bet One" tab.  Each time this button is clicked, a payline will be highlighted or checked.  For instance, on a slot machine with nine paylines and a maximum bet of $5, if a player chooses to play the maximum wager on 3 paylines, they will do so by insuring $5 appears in the stake box and by clicking the "Bet One" button three times.  The total wager on this bet will be $15 on a single spin ($5 x 3).  If the player chose all nine paylines, the wager would be 9 x $5 = $45.  Each payline has its own chance of winning, and will therefore payout on an individual basis according to the payout table. If multiple paylines win at once, the machine will highlight which lines are winners, and will add all the winnings together, displaying the total in a box that says "Win".  (Online slots usually do not show the symbols for all the paylines, especially when more than three lines are picked - However, they will show the number corresponding to each payline on one side of the machine with a line running from the payline number through the the winning combo symbols shown on the playing screen) Because there are more reels and paylines, does not equate to less chances of winning.  The number of symbols and frequency of each, as well as the varied symbol combinations will ultimately effect the odds of winning.  Usually, the more reels there are, the fewer symbols there are composing each reel.  Another point to remember about straight slot machines is that many of them will have a bonus multiplier, which will award a bonus on winning combinations -  but only if all the paylines are bet on a single spin.

After all betting amounts and paylines are settled, the player will click on the "Spin" button.  At this point, all the reels will commence spinning, followed by a display of results and winnings.  Some online slots engage a separate payline at the bottom of a series of multiple paylines, which solitarily spins after the player clicks the Spin tab.  These are called multi-spin slots.  After the results of this single payline are displayed, the player then has an option of putting a 'Hold' on any of the symbols.  If the player chooses to do so, they will click on a button that says 'Hold' directly underneath the symbol. All empty payline spaces of the reel put on hold will then adopt this symbol.  The player will then click the 'Spin' tab again, and all reels not put on hold will begin spinning for the selected paylines.  If the player does not like any of the symbols produced on the initial spin of the multi-spin game, the hold tabs should not be engaged.  Rather, the player would click 'Spin' again, and all reels of the chosen paylines will begin spinning without Holds.

Progressive online slot machines operate according to the same rules and principles, except these slots award winnings based on a percentage of the jackpot, which is networked with thousands of other online slot machines in several online casinos at once.  As would be expected, these jackpots usually climb into the hundreds of thousands of dollars - some in the millions.  The key point to remember about progressive slot machines is that in order to be eligible for the large jackpot, the player must bet the maximum number of paylines and stake amount on a single spin.  If the player hits a jackpot winning combo and did not bet the maximum on the machine, the jackpot will be paid out considerably lower than if all the paylines were staked at their maximum.  This can get expensive - but has the potential of producing large winners.  Usually, the more the jackpot is, the more the betting size is.  Players should find a happy medium they can afford in stake amounts when playing progressive slots.  If this entails selecting a machine with a lower maximum wager, this should be carried through - For the maximum bet is always considered the best option at online slots.  For more on this, please read the slots strategy section.

Here is a compilation of online slot machines you may find on the internet.  They are categorized by maximum payout and wager sizes.  Progressive machines and multi-spin slots are noted:
 

Additional Slots Tips and Information:

• Picking Online Slots According to Stakes

• Progressive Slots Strategy

• Identifying Casino Slots in a Las Vegas Casino

• Gambling Single Coins at Multiplier Slots

• Betting the Max at Progressive Slot Machines

• Introduction to Slot Machine Symbols

• More Online Slot Machine Symbols

• Spin the Reels Slow at Casino Slot Machines

• Introduction to Spinning Reel Online Slots

• The Basics of Option-Buy Casino Slots

• Coin Multiplier Online Reel Slot Machines

• Differences Between Reel and Video Slots

• Payout Percentage is Important at Online Slots

• Using Hit Frequency to Gauge Bankroll Strain

• How to Peruse and Learn Online Video Slots

• How to Search Out Land-Based Casino Slots