Windows Vista

Microsoft claimed Windows Vista is off to a fast start, having sold more than 20 million copies since its January 30 consumer release. By comparison, in its first two months, Windows XP sold 17 million copies.When XP made its debut in 2001, it came in two main flavors--Home and Professional. The company eventually added the Tablet PC and Media Center editions, and over time, Media Center became the dominant version on retail shelves. Vista comes in six flavors--Home Basic, Home Premium, Business, Enterprise and Ultimate, as well as a Starter Edition only sold on new PCs in emerging markets.