Ballmer described Windows 8 as the "deepest, broadest and most impactful" Windows software ever created by Microsoft, despite 2009's Windows 7 proving a big hit with businesses and consumers, reports AFP.
Speaking at the Seoul Digital Forum, he said: "It's really, in some senses, a dawning of the rebirth of MS Windows. It's certainly the most important piece of work we've done."
Windows 8, currently in open beta with a preview version due in June, has been created to work on both desktops and tablet computers, via its Metro user interface optimised for touchscreen devices.
The system also more closely integrates Microsoft's SkyDrive cloud computing service, allowing users to store and share personal data and files across various devices.
Microsoft has high hopes that Windows 8 will help stimulate struggling global PC sales, offset the rising popularity of Apple Macs, and also power a new generation of tablet computers to compete with devices running Apple's iOS and the Google Android mobile OS.
"The number of core (cloud) platforms, around which software developers will do their innovation, is not ever-broadening," he told delegates at the forum.
"It's really a quite smaller and focused number - Windows, various forms of Linux, the Apple ecosystem."
The Microsoft chief executive believes that in three to five years "there will be just a few ecosystems that really can get the critical mass".
Ballmer also gave the bullish prediction that up to 500 million users will have Windows 8 by next year, and promised the "best economic opportunity" for device makers and app developers adopting the operating system.
He also said that Microsoft will soon introduce Skype for Windows 8, after Microsoft acquired the internet telephony provider for $8.5 billion (£5.5bn) last year.