Windows 10 Is Off To A Good Start
According to the data, Windows 10 reached a global market share of 5.2% in its first full month on the market, topping the launch performances of Windows 7 and Windows 8, which had claimed 4.1% and 1.1% market share in the first month after their respective releases.
It's still early, but it appears that Microsoft's decision to scrap some of the more radical changes introduced with Windows 8 resonates well with PC users around the world. The fact that Windows 10 is given away for free to Windows 7 and Windows 8 users undoubtedly also helps to speed up the rate of adoption.

Description
This chart shows global market share of desktop operating systems in August 2015.