Microsoft may be sending its PC vendor partners early versions of the Windows 8 operating system.

Citing anonymous sources, Microsoft enthusiast site WinRumors says that Hewlett-Packard, among other vendors, are currently receiving Milestone 3 build 7971.0.110324-1900 of Windows 8 through Microsoft's Connect testing system. CNET sister site ZDNet reported back in January that its own sources said Windows 8 was at the Milestone 2 mark at that time.

Microsoft is working on Windows 8 as Windows 7 continues to perform extremely well at retail. The software giant announced earlier this year that Windows 7 is the fastest-selling operating system ever released, tallying over 300 million licenses sold through 2010.

On the Windows 8 front, Microsoft has been relatively tight-lipped. However, the company did say back in October in a blog on its Dutch Web site that Windows 8 will be available in 2012.

At the Consumer Electronics Show in January, Microsoft revealed that the next version of Windows would be capable of running on ARM architecture in addition to x86 architecture. Nvidia, Qualcomm, and Texas Instruments were specifically cited as Microsoft's ARM partners at the time.

Beyond that, much of the speculation surrounding Windows 8 has come by way of leaks.

Last summer, a group of slides labeled "Microsoft Confidential" hit the Web discussing some of the features that might be making their way to the next version of Windows. They included face recognition, faster boot-up times, and a focus on 3D capability.

Those slides were followed by a report from BusinessInsider last month, citing its own sources who said that Microsoft wants to show off tablets running Windows 8 over the summer. A leaked "tablet road map" from Dell that surfaced last month, as well, indicated that the company was planning to release a Windows 8 tablet, codenamed "Peju," in the first quarter of 2012.

In an e-mailed statement to CNET, a Microsoft spokesperson said that the company is "not commenting on future versions of Windows."

Updated at 8:53 a.m. PT: to include Microsoft comment.