There were few surprises at Thursday's launch event because Microsoft Corp. has been previewing preliminary versions of Windows 8 for the past 13 months - part of 1 billion hours of testing.
Still, the overhaul poses a big risk for the Redmond, Washington, company because Windows 8 looks and operates so much differently than previous versions.
"This is the biggest gamble they've ever made," said analyst Richard Doherty of the Envisioneering Group. "Does (Windows 8) do more things? Yes ... but it's not that easy to use."
Even when users revert to a desktop mode, the redesign discards the familiar "start" button and menu that Windows has had for 17 years, a change that critics believe will almost certainly provoke howls of protest.
But many reviewers applaud Microsoft for greeting users with a mosaic of tiles displaying applications instead of relying on the desktop icons that served as the welcome mat for years.
Image: Ballmer walks in front of a screen of computer manufacturers after his presentation at the launch of Microsoft Windows 8.