"I wanted to affectionately call this 'not an iPad,'" Sinofsky said of the prototypes. "I'm also calling this not the first Windows 8 computer and not for sale."
Although Windows 8 will compete with the iPad, it takes a much different path. As Microsoft has been telling the world for months, in bits of information about the new OS, Windows 8 rejects the app icon look of iOS and Android for its own "Metro style" of live tiles seen on Microsoft's 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.
For one thing, Windows 8 on a tablet isn't limited to a touchscreen. It works with a mouse, a keyboard and a stylus as well as your fingertips. The test tablets, handed out by Microsoft, are quick and responsive and offer true PC-like specs in a tablet body.
Windows 8 will run traditional desktop apps that will be better suited for a mouse, such as Adobe Photoshop, and touch-centric apps, a few of which were previewed Monday and which Microsoft hopes will inspire developers this week at Build.
Apps, of course, will be the key to making Windows 8 a success on tablets.
Since the iPad hit the market, Apple has sold more than 25 million of the blockbuster devices. Google's Android operating system is Apple's only serious competitor in the tablet space but hasn't been able to slow the iPad's growth much thus far.
Windows 7, released in 2009, has sold nearly 450 million copies thus far and as of last Thursday in the US, is more widely used than the stalwart Windows XP, Sinofsky said.
On PCs, Windows 8 will run all Windows 7 applications, according to the company. But Windows 7 applications may not run on Windows 8 tablets built with ARM processors.
"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.
Monday's presentation offered a look at about 30 apps running on Windows 8 test tablets and on PCs. All of the apps were "written in 10 weeks by teams of two or three college interns", Sinofsky said. "That kind of gives you the idea of the power of the platform."
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