Windows 8 is the "dawning of the rebirth of Microsoft Windows," according to Microsoft CEO Steve Ballmer.
He also called it the "deepest, broadest, and most impactful" version of Windows ever.
The man isn't shy, and has been known to get a little excited about Microsoft products in the past, but backed up these claims with some estimates.
"We've just passed the 500 million licenses sold mark for Windows 7, which represents half a billion PCs that could be upgraded to Windows 8 on the day it ships. That represents the single biggest platform opportunity available to developers," said Ballmer.
Referring to Windows 8, he added: "It's certainly the most important piece of work we've done."
Ballmer was speaking at the Seoul Digital Forum.
He also threw in his thoughts on cloud computing, saying it would come to be dominated by a few big players. "The number of core [cloud] platforms, around which software developers will do their innovation, is not ever-broadening," he said.
"It's really a quite smaller and focused number - Windows, various forms of Linux, the Apple ecosystem."
In three to five years, "there will be just a few ecosystems that really can get the critical mass," he added.
Windows 8 will work on tablets and PCs. It's expected to boost sales of ultrabooks and other laptops when it goes on sale around October. Microsoft should finish working on the operating system sometime next month.
Last week, Microsoft showed off the new home screen for Windows 8, doing away with the gloss and reflections found in previous incarnations.