The Microsoft co-founder and chairman, speaking in a video interview with Microsoft's Steve Clayton, echoes CEO Steve Ballmer in calling Windows 8 an "absolutely critical product" that combines "the best" of tablets and traditional PCs.
Gates noted that people will be "amazed at the energy" Microsoft is putting behind its new products, and he said Windows 8 "is key to where personal computing is going."
"This is the big time for us," Gates said.
He added that he has been using his Surface tablet nonstop, calling it "unbelievably great."
Gate also hinted that the PC/tablet version of Windows and the phone version will eventually merge over time.
"We're certainly sharing between Windows 8 and Windows Phone 8," Gates said. "Over time, we do more and more of that. It's evolving literally to be a single platform."
Windows 8 is the first version of Microsoft's operating system to incorporate touch capabilities and other features commonly found on tablets. Many of the devices being touted by PC makers are so-called hybrids or convertibles, which sometimes allow the screens to detach from keyboards. The companies are counting on Windows 8 to help them compete with the iPad and other popular tablets.
Microsoft co-founder Paul Allen weighed in with some Windows 8 observations of his own earlier this month. In a blog post, he concluded that the new tablet features of Windows are "particularly bold and innovative," but he called some aspects of the new operating system "puzzling."
Microsoft launches the new operating system later this week.