"We are going to innovate with a challenger mindset," said Nadella in a question and answer session at the developer conference. "We are not coming at this as some incumbent trying to do the next version of Windows, we are going to come at this by innovating in every dimension."

Time to get smart

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Nadella did not have a snappy answer to the question of what Microsoft's overarching mission now was, after it had achieved its original goal of putting a computer on every desk and in every home. Instead he elaborated on remarks he made last week about the importance of mobile devices as everything we do becomes digitized and connected to the internet.

"Our vision, simply put, is to thrive in this world of mobile first, cloud first," said Nadella. "Our goal is to really build platforms, create the best end-user experiences, the best developer opportunities and IT infrastructure for this ubiquitous computing world."

SIRI rival

Also at the gathering, Microsoft formally announced it has developed a voice activated phone assistant feature called Cortana, a direct rival to Apple's Siri.

The feature has been rumored for some months and a test version was demonstrated at the event by Joe Belfiore, a Windows Phone executive.

The Cortana service, which can take verbal instructions to search the Web, set alarms, make calls and a host of other actions, is still in beta testing but will soon be a standard feature on Windows phones, said Belfiore.

He announced that the latest version of Microsoft's smartphone software, called Windows Phone 8.1, will be rolled out to consumers as a downloadable upgrade in the next few months, and new phones running the software will be in stores by late April or early May.

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