Microsoft called it a "reimagining" of Windows that will run on all types of devices from small, touch-sensitive screens to traditional large-screen PCs, and be able to work either with a keyboard and mouse, or without.

It is intended partly to make Microsoft a contender in the emerging tablet PC market, where its current Windows 7 operating system has struggled to compete effectively with operating systems from Google, Apple and others. But the new interface is intended for use on all types of PCs.

Microsoft showed several prototype systems on stage running the software, including a tablet, a laptop and an all-in-one PC. The new interface is a significant departure from the traditional Windows desktop that Microsoft has relied on for decades.

The screens showed large, colored application icons that look in a way similar to those on Microsoft's new Windows Phone 7 OS. Tapping an icon with a finger launches the application and allows it to take up the entire screen, without the usual Windows menus, system tray and scroll bars around the edges of the screen.

"The application comes quickly to life as Windows fades to the background," said Michael Angiulo, corporate vice president of Windows planning, hardware and ecosystem, who demonstrated the new software here.