With patch 4.0.1, we will be introducing a new World of Warcraft launcher that will allow you to stream game data while you play. This will reduce the time you spend downloading, installing, and patching World of Warcraft. Streaming Launcher Basics
We've redesigned the launcher to provide a visual update to your installation progress. You will see a new progress bar with sections (Red, Yellow, Green) that represent the amount of data you have currently installed.
There are three stages of download progress: Setup (Red):
Core game content is being prepared. You cannot enter the game at this time. Available (Yellow):
Major game content is not completely applied. You can play, but your game experience will not be ideal. Playable (Green):
Final game content is almost complete. You may experience a few issues with playing at this stage.
All World of Warcraft data will continue to download and apply whether you wait in the launcher or are playing in-game. If you find the play experience unsatisfactory, you may exit the game and allow the Launcher to continue the download. While the launcher should automatically adjust the download according to your bandwidth, this may improve the play experience for users with low bandwidth Internet connections. Streaming Launcher FAQ
For more information, please refer to our FAQ: http://forums.worldofwarcraft.com/thread.html?topicId=27188059042&sid=1&pageNo=1#1