Since 2002, when Microsoft introduced Windows XP, its signature operating system has proved to have more stamina than anybody would have originally thought. Despite missteps in Vista, that OS still managed to introduce useful new features and set the stage for Windows 7.
This chart provides a rundown of some of the major features introduced in each Windows iteration, as well as a quick look at the minimum hardware requirements for XP, Vista and 7. Keep in mind that Windows 7 is still in its testing phase, though it's not expected that other major features will debut before it's released during the coming holiday season. You can download the Windows 7 release candidate here.
Full feature here - Contrasting Windows: New feature comparison - CNET Asia