Microsoft explains how to count to 7
It turns out, that not all Windows operating systems are created equal. So while Wikipedia lists 25 version of Windows (not counting Microsoft Bob), Microsoft doesn't count each and every one of those releases as a separate version of Windows.
Here's how it works: Microsoft gives a version number to each operating system. First there was Windows 1.0, then Windows 2.0, then Windows 3.0. Forget all the point numbers like 3.11 for a moment. Because the next major release was Windows 4.0, which is better known as Windows 95.
Every operating system up through Windows ME was built on the Windows 4 code, and it wasn't until Windows 2000 that Windows hit 5.0.
Windows Vista was version 6. And the next OS will be Windows 7.
So ignore Windows 98, Windows 98SE, Windows Home Server 2008, and pretty much everything you thought you knew about Windows. Because Windows 7 is the seventh version of the operating system.