The faster Windows operating system is XP. Vista is awaiting its first service pack 1 
to clear up its bugs. While consumers are trying to patch up their Vista computers, Microsoft is forced to update Windows XP to service pack 3 for loyalists and those who have rejected Vista.
Studies have shown, that with the same speed processor and RAM, Windows XP clearly is faster than Windows Vista. A bechmark test run by New York Computer Help has shown Microsoft Outlook 2003 to run tasks 2.5x faster in XP than Vista. 
Vista was proven to be as fast as XP when the RAM in Vista was doubled (2GB in Vista versus 1GB in XP). These test results were performed with and without the new service packs in both systems so the service packs have no affect either way.
For performance reasons and overal glitches in Vista, XP is still the clear winner here. That is why Microsoft has extended the time computers are still able to be purchased with Windows XP.
