Microsoft sells 400 million licenses for Windows 7

Windows 7 continues to charge ahead as a successful operating system release for Microsoft. CEO Steve Ballmer revealed in a Monday keynote at the annual Worldwide Partner Conference in Los Angeles that the number of licenses sold worldwide has now surpassed 400 million.

Microsoft's latest version of Windows already runs on a little over 27 percent of all worldwide computers, according to data from Net Applications. Even though Windows 7's share has nearly doubled in the past year, it still has not been able to unseat the market leading Windows XP, still running on over half (51 percent) of all PCs.

The long-tail success of XP, now 10 years old, has given Microsoft a good deal of trouble in attempting to push users to a newer version. The company has attempted to force users to upgrade by ending support for Windows XP SP2 last year, and will completely phase out XP with the expiration of support for SP3 in 2014.

Indeed, the company is served well by making a big deal of the end of XP. In a message to its business customers Monday, Microsoft announced that the life cycle of XP would end in 1,000 days and urged businesses to begin migrating to Windows 7 now.

"Windows XP served us well, but in the ten years since it launched, the world has changed," Microsoft's Erwin Visser wrote in a blog post. "It's time to retire Windows XP and move to Windows 7 to take advantage of the last decade of innovation in areas such as security, performance and more natural, intuitive interface."

It may sound strange that Microsoft would push Windows 7 to businesses when Windows 8 is due in 2012. However, the company seems to be prepared to deal with a dual OS world as its partners incorporate Windows 8 into newer devices that it has been optimized for -- such as tablets -- and work alongside Windows 7 PCs.

"Windows 7 is the path to Windows 8," corporate vice president and chief financial officer of Windows Tami Reller said on stage alongside Ballmer.