Microsoft has charted unprecedented sales figures for its still-fresh Windows 8 operating system in its first month of availability, Microsoft executive Tami Reller said today.

“The journey is just beginning, but I am pleased to announce today that we have sold 40 million Windows 8 licenses so far,” Reller said at the Credit Suisse 2012 Annual Technology Conference.

In a blog post, Microsoft claims Windows 8 is outpacing Windows 7 in terms of early-stage upgrades.

Previously, Microsoft said it sold 4 million Windows 8 upgrades in its first three days of availability, so it appears the pace of people upgrading and purchasing Windows 8 PCs and operating system upgrades has kept up throughout the month.

One factor that may be driving Windows 8 licence sales is that it only costs $40 to upgrade a Windows XP, Vista, or 7 PC to Windows 8. The $40 upgrade offer ends on January 31.

Reller, one of two execs tapped to fill Windows president Steven Sinofsky’s shoes after he exits Microsoft, did not announce any additional sales figures. Most notably, we’d like to know how many Surface tablets have been sold to date.