In a brief interview Thursday, Ballmer expressed confidence that PC users would quickly realize the mosaic is easier and quicker to use than the old desktop format.
"You've got a whole screen as a start button!" he said.
Windows 8 comes with new controls.
It marks the first time Microsoft has made touch-screen control the top priority, though the system can still be navigated with a keyboard and mouse in desktop mode.
"In the case of Windows 8, seeing, touching, clicking and swiping is really believing," Ballmer said.
He also predicted that PCs running on Windows 8 would be hailed as the best machines ever made.