The sales number represents a solid but unspectacular start for the touch-friendly operating system designed to combat Apple Inc's and Google Inc's domination of mobile computing, which has shunted aside PCs in favor of iPads and smartphones.
Tami Reller, finance and marketing head of the Windows business, did not give a precise comparison, but sales of 40 million licenses for Windows 8, launched on October 26, appear to be ahead of Windows 7, which sold just over 60 million units in the first 10 weeks on sale at the end of 2009.
Reller did not break down the Windows 8 license sales between relatively cheap upgrades and purchases of new machines running the new software, but suggested much of the growth was coming from upgrades.
"Windows 8 upgrade momentum is outpacing that of Windows 7," said Reller, speaking at an investor conference held by Credit Suisse. Upgrading to Windows 8 costs $40, compared to $70 for the full software package or hundreds of dollars for a new PC.
The latest figure does not mean that 40 million users have adopted Windows 8. Many of the sales are to PC manufacturers, who in turn sell a large number of machines to companies, very few of which are using Windows 8 yet.
According to tech research firm StatCounter, about 1 percent of the world's 1.5 billion or so personal computers making a total of around 15 million are actually running Windows 8.
Reller did not disclose sales of Microsoft's new Surface tablet, its first-ever own-brand PC, designed to challenge the iPad head on.
The first Surface, based on a chip designed by ARM Holdings Plc, does not run old versions of Microsoft programs. A slightly bigger version based on an Intel Corp chip that will run the full Windows 8 Pro operating system and be fully compatible with the Office suite of applications will be available in January, Reller said.
The investor conference was the first public appearance for Reller since she was named as one of two executives to run the Windows unit after president Steven Sinofsky unexpectedly left two weeks ago. Julie Larson-Green heads the engineering side of Windows.
Reller said the Windows unit had survived Sinofsky's surprise departure.
"The team holistically is in great, great shape. And the product is in great shape," she said, responding to a question from a Credit Suisse analyst. "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."
Earlier in the day, Microsoft said it had sold more than 750,000 Xbox game consoles in the United States last week, including the day after Thanksgiving, one of the country's biggest shopping days.
That is down from 960,000 sales in the same week a year ago, in line with reduced computer game spending across the board this year, as gamers hold off on purchases in the tight economy and move toward free online games.
© Thomson Reuters 2012