How World of Warcraft Works

The Game Client

Blizzard applies patches to "World of Warcraft" to fix game issues and add new content.
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The "World of Warcraft" program you install on your computer is the client, which has four primary duties. The client:

  • decodes and displays the data that make up the game world, as well as the user interface (UI) and any associated addons.
  • receives input from you and from a remote server and changes the game display accordingly.
  • gives feedback to you and the server, based on what's happening in the game.
  • keeps up with any changes you make to your game's layout and settings.

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.