Chrome OS was announced to much fanfare last week, although it has yet to be demonstrated, and Google is already enjoying much success with its open-source Android platform for mobile devices.
Ballmer said in an onstage Q&A session following his speech at the Microsoft Worldwide Partner Conference in New Orleans yesterday that Google is making the same mistake as Microsoft did in the days when it produced Windows NT and Windows 95.
"I don't know if they can't make up their mind, or what the problem is over there," he said. "The last time I checked you don't need two client operating systems."
Ballmer also ruled out Microsoft creating a new operating system.
"What we need to do is continue to evolve Windows, Windows applications, Internet Explorer, the way IE works in totality with Windows, and how we build applications like Office," he said. "We need to make sure we can bring our customers and partners with us."