Microsoft gave developers a taste of its new OS at the company's Build conference on Tuesday in California when Steven Sinofsky, president of Microsoft's Windows team, offered a full preview of its upcoming Windows 8.

"We re-imagined Windows," said Sinofsky, to the thousands of developers gathered in the conference in Anaheim, California. He added that Windows 8 completely revamps the existing OS found in millions of computers worldwide from the chip level to the UI.

Windows 8 is expected to be the company's answer to Apple's iOS. The new OS was shown running on three tablets, an ARM-based Samsung tablet, a tablet running on NVIDIA's quad-core Tegra 3 chipset and a Qualcomm tablet.

The presentation which is about getting developers a first look at Windows 8 and to give them the chance to start writing new apps for the OS, gave a detailed first look at the features in Windows 8.

"I wanted to affectionately call this 'not an iPad,'" Sinofsky said of the tablets presented. "I'm also calling this not the first Windows 8 computer and not for sale."

Although intended to compete with the iOS, Windows 8 will not have the app icon look of other tablet operating systems. It will have its own "Metro style" of live tiles seen in the Microsoft Windows Phone 7 OS.

"We have a different point of view on how touch works and we have a different point of view on how apps work and it's been deeply thought out," said Jensen Harris, the director of program management for Windows.

Windows 8 will work with a traditional mouse and keyboard set-up as well as a touchscreen. The test tablets had faster boots times and could synch with any Windows 8 device. PC users can still use the Windows 8 to run older Windows 7 applications as it is backwards compatible.

"All the existing desktop apps will continue to run in the desktop environment," said Julie Larson-Green, a Windows corporate vice president. "Metro apps will be a separate thing" and run on all Windows 8 machines - tablets and PCs.