How World of Warcraft Works

As of July 2007, "World of Warcraft" had more than 9 million active subscribers worldwide [source: Blizzard, press release]. While there's no publicly-available, comprehensive census of exactly who plays the game, there are several researchers who have studied WoW players extensively.

Researcher Nick Yee has used online surveys to poll "World of Warcraft" players about themselves and their characters. These responses come from a self-selected group, or people who have decided for themselves to visit Yee's Web site and fill out the survey. This means that the results may not represent the world's demographics as accurately as a random sample would. Instead, it may reflect a particular subset of players -- those who are serious enough about the game to research it online and to feel motivated to spend time answering questions about it.

According to one of Yee's 2005 studies, 84 percent of "World of Warcraft" players are male, and 16 percent are female. The average player's age is 28, and female players tend to be a few years older than male players. Regardless of their gender, players spend an average of 21 to 22 hours a week playing the game [source: Yee, WoW Demographics]. Of course, these statistics may have shifted since Yee collected his data. You can learn more about Yee's research at The Daedalus Project.

The amount of time people spend in the game world depends in part on their characters' levels. According to research conducted at the Palo Alto Research Center in 2005, players tend to put in an extra burst of playing time when a character is about to reach a milestone level. At the time of the study, players gained access to a mount, such as a horse, tiger or kodo, at level 40. The study showed a spike in play time leading up to level 40 that was even greater than the spike leading to level 60, which was the highest possible level when the study was conducted. However, once people reach the highest levels, they generally spend more time playing than they did at lower levels [source: PARC, Playing Time]. Now, players gain mounts at level 30 and top out at level 80 with "Wrath of the Lich King" installed.

These numbers relate to one of the reasons people play "World of Warcraft" and similar games -- for the feeling of accomplishment that comes from in-game achievement. But there are also other reasons for participation in the online world, including:

Researcher Richard Bartle placed these four types into four categories, described as achievers, socializers, explorers and killers. This has become a commonly-used model for describing how and why people participate in role-playing games.

You can also describe "World of Warcraft" players in terms of which activities they participate in while playing. Hardcore raiders spend most of their time in high-level dungeons. Other players spend most of their time in player-versus-player (PvP) environments. Some PvP enthusiasts are twinks, or players who advance to a particular level and then acquire lots of gear that will make them more powerful than other players of the same level. Then, there are the casual players, who may enter raid dungeons and PvP battlegrounds but who don't spend their game time focusing on them exclusively.

Regardless of exactly what people are doing in the game, they're using the same basic tool to access the world -- a computer. Next, we'll look at the "World of Warcraft" client and how it runs.

The "World of Warcraft" program you install on your computer is the client, which has four primary duties. The client:

The client gets a large portion of its data from archives stored on the computer's hard drive. Much of the visual information is stored in MPQ format, an archive format proprietary to Blizzard. Sounds are generally stored as WAV or MP3 files. As players move through the world, the client caches some of this information in a folder for faster access.

The client isn't static -- it changes as the game develops. Blizzard releases patches to "World of Warcraft" to fix bugs, adjust game play issues and add new content, like quests and dungeons. Lots of players access the game world simultaneously, and each one has to be able to see the same features and operate under the same rules. For this reason, Blizzard pushes new patches to each player's computer. When you open your game after a new patch has been released, your client will automatically download and install the patch. Blizzard's background downloader can also download pieces of the patch that are ready for release ahead of time to cut down on the amount of time it takes to get a patch.

Separate from the client, but related to it, is the game launcher. The launcher is a small program that provides hyperlinks to new information at the Blizzard Web site. It also lets you know when new patch information is ready to download and opens your game itself. The launcher can also check your computer for viruses, hacks and cheating software and warn you if it finds them.

Once you launch the program and log in, the client begins to recreate the game world. We'll look at what happens on the next page.

Let's examine the image below as an example of how the "World of Warcraft" game client works. In it, a shaman named Yellowbell is collecting a stone for a quest, but she's caught the attention of a goblin, which is on his way to attack her. Here's what's happening from a client perspective:

These are just the highlights. The client constantly accesses or receives information about the game world and the characters in it. The more other characters there are nearby, the more work the server has to do. This is why some players' games can slow to a crawl in highly populated areas -- the computer's CPU and video processor can't keep up with all the information they need to display. In some cases, the frame rate, measured in frames per second (FPS), can drop dramatically, causing players to see the world as a series of still pictures rather than a moving scene.

The client also stores information about your character and your in-game options in the WTF folder on your hard drive. Files in this folder are usually in one of three formats:

We'll look at Lua -- the language used to create "World of Warcraft" addons -- on the next page.

"World of Warcraft" has lots of ways for you to customize your game. You can access lots of settings through your interface options. These options let you change how your camera moves, which features your game displays and how you use your mouse to target yourself or enemies. Your video options lets you change the level of detail in the game world, which can help compensate for a slow processor or limited graphics abilities.

But suppose you want to completely change the way your party's health and mana bars look when you're in a group or see how much money you have without opening your backpack. The WoW interface options can't handle these requests -- but third-party addons can.

Addons are downloadable additions to "World of Warcraft" that players create. You can find addons at sites like Curse, WowAce and WowInterface. Here are some popular addons and what they do:

Addons are created using the Lua scripting language. When you download them, they look like folders full of files. Some files are LUA format, while others are extensible markup language (XML) or table of contents (TOC) files. To install the addon, you simply move its entire folder to the correct location on your computer. These are the default locations:

This makes the addon a part of your game's file structure, which changes how the game operates. You can also download programs that will update your addons for you.

There are a few things to keep in mind if you're using addons:

As long as they don't play the game or make in-game decisions for you, addons don't generally break the rules. Other exceptions are addons that affect the way your computer communicates with a remote server and packet sniffers, or programs that track the way information travels between the client and the server. We'll look at the remote server and how it works in the next few sections.

Many players think of "World of Warcraft" servers in terms of world servers, or realms. These are essentially complete, self-contained copies of the game world named after people and places in Warcraft lore. There are about 200 realms in North America and other realms in different parts of the world. Playing the game on servers not owned by Blizzard or one of the companies that hosts official servers in Asia is a violation of the terms of use.

The realms come in three primary types:

You can make characters on lots of different servers, but characters can't communicate across servers unless they're in the same player versus player (PvP) battleground.

A world server isn't a single server, though -- it's a collection of servers. As of 2006, Blizzard had about 9,000 servers around the world [source: Vivendi].

When you log on to your "World of Warcraft" account, you do so using an authentication server. This server verifies your name and password before transferring you to the realm on which you last played. Exactly which portion of the server you access depends on where you logged out of the game. Blizzard hasn't disclosed the exact architecture of its world servers, but based on the game's behavior, several server divisions are clear.

Each of the world's three continents -- Kalimdor, the Eastern Kingdoms and Outland -- has its own servers. There's also a separate server for instances, or the game's dungeons. When a group enters an instance, the game spawns a copy of that dungeon for the group. Other groups and players can't enter it. A database server, or a database function running within the servers, provides information on the locations and respawn time all of the items players can loot (pick up) or otherwise interact with in the game world, including:

These items persist across all the servers that make up the realm. Some chat channels, like group and guild chat, are also accessible no matter where you are in the game world. Others, like general cannels for specific regions within the game, are accessible only when you're in that particular zone.

Everything about your particular character, including the quests you've completed, your level and all your gear, is stored in a database that's tied to your "World of Warcraft" account. You can log in from any computer that is running the game and find your character exactly the way you left it. This database can also interface with a Web server, allowing you to do things like look at other players' gear and your own at the "World of Warcraft" armory. You can also pay a small fee and have your character moved from one server to another -- Blizzard adjusts its database accordingly.

To play the game, your computer has to communicate with one of these sets of servers. We'll take a look at what happens on the next page.

All the maps and scenery in "World of Warcraft" live on your computer, but information about what's going on in the world has to come from a server. Based on the information it gets from your game client, the server performs a lot of calculations about the world, including:

The server also collects information from other players clients' -- whether you're in a group with them or not -- and relays it to your computer. This allows you to see other characters, their gear and their actions in the game. It also lets you receive chat messages, guild invitations and group invitations. This information doesn't travel directly from another user's computer to yours -- it travels to you via the server.

The efficiency of all of these interactions is dependent upon the amount of time it takes a message to travel from a client to a server and back. Players who experience high latency -- or a long travel time -- can see significant delays between when they perform an action and when they see it happen on the screen.

A battle against a mob is an ongoing exchange of information between your computer, the computers of the people in your group and the server. For example, say you and some friends plan to Doom Lord Kazzak, a raid boss in Outland. Here's what happens:

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PvP combat is a little different -- the server still makes calculations, but other players, rather than artificial intelligence, control the other combatants. But regardless of whether an AI script or a human brain is in charge, the battle itself can often be challenging.