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Although many of the new features have been shown off already, the conference offers the company a chance to explain some of the reasoning behind the update and sell developers on Microsoft's ambitions to regain relevance lost to Apple's iPad and various devices running Google's Android software.
Windows 8, which was released Oct. 26, was meant to be Microsoft's answer to changing customer behaviors and the rise of tablet computers. The operating system emphasizes touch controls over the mouse and the keyboard, which had been the main way people have interacted with their personal computers since the 1980s. But some people have been put off by the radical makeover. Research firm IDC blamed Windows 8 for accelerating a decline in PC shipments worldwide.
Microsoft's event is taking place at The Moscone Center in San Francisco. The keynote kicked off shortly after 9 a.m. PDT.
Here's a running account of the event, presented in reverse chronological order. All times are PDT.
Presenters include CEO Steve Ballmer; Julie Larson-Green, corporate vice president for Windows; and Antoine Leblond, corporate vice president for Windows Web Services; and Gurdeep Singh Pall, corporate vice president for Bing.