March 18, 2009 Patch

Added Multicore Rendering

• This initial release is aimed at testing compatibility, so the option is OFF by default
• To turn it on, go to the Options->Video->Advanced dialog, and check the "Multicore Rendering" option

Other Changes

• Several performance improvements to decals and client bone/flex setup
• A variety of alt-tab and mode switch fixes
• Improvements to the way the engine initializes surround sound, fixing some specific hardware cases
• Fixed a crash on exit in Vista 64

Source: http://store.steampowered.com/news/2359/