Microsoft is experimenting with a free version of Windows.

Offering Windows 8.1 for free or very low cost for users of Windows 7 would boost the numbers of people using the latest version of Microsoft's signature software.

Sources who say they're familiar with the company's plans say it's building a new "Windows 8.1 with Bing" that would bundle several Microsoft apps and services, and the aim is to bring a low-cost version to market, perhaps even offering it as a free upgrade for Windows 7 users.

The sources say the idea is designed to push and monetize Microsoft’s cloud services and apps.