but why does winver displays version as 6.1? build 7600.

just asking. ^^

The version history of the various Windows families goes like this:

1. Windows 3.0 and 3.1 (and Windows for Workgroups 3.11) from the early 1990s used the version numbers as part of their name. The first releases of Windows NT, also from that era, followed suit, with Windows NT 3.1 and 3.5.
2. Windows 95 was technically version 4.0. Windows NT 4.0, which was released exactly a year after Windows 95, adopted the Windows 95 interface. Windows 98 was version 4.10.1998 and Windows 98 Second Edition was 4.10.2222A. The much-maligned Windows Me was 4.90.3000. (History lessons here and here for those who care.)
3. Windows 2000 was the first release in the version 5 family. It was followed by Windows XP, which was version 5.1. Service packs are identified by build numbers, but service packs do not affect the version number.
4. Windows Vista was Windows 6.0 (Vista Service Pack 1 is build 6001). Because the next release of Windows is going to be based on the same kernel as Windows Vista, it should have the version number 6.1. Indeed, every copy of Windows 7 that has leaked to public view so far has had a build number of 6.1.xxxx. This numbering is almost certain to remain in the final product. If the major version number changed to 7.0, many applications written for Windows Vista would fail to install or run properly, simply because of version checking.