As expected, the newest version of Windows is a hot seller. The first month since its release, Windows 8 sold 40 million licenses. That’s double than what Windows 7 sold three years ago.

Microsoft has been building momentum for the Windows 8 release for months. It worked. The company sold 40 million Windows 8 licenses in the first four weeks since the release. Although, Microsoft executives haven’t revealed if it was the purchase of gadgets with Windows 8 pre-installed or of the software itself, but according to Tami Reller, finance and marketing head of the Windows division, the 40 million licenses were mostly upgrades.

“The journey is just beginning, but I am pleased to announce today that we have sold 40 million Windows 8 licenses so far” said Tami Reller, the corporate vice president for Microsoft. She added that the “Windows 8 upgrade momentum is outpacing that of Windows 7”. Windows 7 sold slightly over 60 million licenses during its first 10 weeks on the market.

It’s not a brainer: an upgrade to Windows 8 costs $40. Add $30 and you get the whole package. Compare that though with a new device that costs several hundred dollars. And given that the 40 million Windows 8 licenses were mostly sold to PC manufacturers, within the next four weeks, it’s very likely the sales will be even higher, as consumers prepare for their holiday gift purchases.

Microsoft’s Windows 8 Surface tablet has been getting a lot of attention lately as it has been promoted as one of the best contenders to the iPad. The company hasn’t disclosed how many of the 40 million Windows 8 purchases were Surface tablets. It might still not account for that much, since Microsoft announced there’s another version of the tablet to be released, a more powerful one that will hit the markets in January.

For Tami Reller, Windows 8 is a huge bet. She is one of the two executives that took over the Windows division after president Steven Sinofsky left the company just two weeks ago. Reller says that the president’s departure didn’t impact the team and product, which are both in “great, great shape”.

“I think transitions are always somewhat of a challenge, but I think that timing-wise it is a reasonable time, and the team is busy” she added.