Now Windows 8 is available to hardware makers that will release new PCs and tablets with the OS at the end of October, when the product officially starts shipping commercially.

"Together we are bringing to customers a new PC experience that readies Windows PCs for a new world of scenarios and experiences, while also preserving an industry-wide 25-year investment in Windows software," wrote Steven Sinofsky, president of the Windows and Windows Live Division wrote in a .

Now it's crunch time for Microsoft. "Obviously, this is not the end, it's just the beginning," said Gartner analyst Michael Silver. "Now Microsoft -- and all its partners -- need to execute all of it."

Windows 8 will run on devices with x86 chips from Intel and AMD, as well as on devices that use ARM chips. The ARM version of the OS is called Windows RT.

After hitting this RTM (release to manufacturing) milestone, Microsoft is reiterating the Oct. 26 date for the commercial availability of the OS in new devices as well as in stand-alone form as an OS upgrade on existing Windows PCs.