StatCounter claims that the Microsoft operating system is now powering 50.2% of the world's computers, compared to the 29.9% of the 11-year-old Windows XP.
The once-dominant Windows XP has been in steady decline for some time, but remains in the runner-up spot with a significant lead on the poorly received Windows Vista.
Apple's Mac OS X accounts for less than 10% of the market, but is now within touching distance of Windows Vista.
Windows XP is expected to continue on its downward spiral following Microsoft's announcement that it will cease support for the operating system in 2014.
Microsoft will release its next generation Windows 8 operating system later this year.