Windows Me was still in 95/98 development line and is internally versioned as 4.2. 2000 and XP were 5.x, Vista was 6.0, Windows 7 was 6.1, Windows 8 was 6.2, and Windows 10 probably would have been internally 7.0 if they hadn't bumped the internal number forward to match.

https://en.wikipedia.org/wiki/List_of_Microsoft_Windows_vers...