The Promise of Windows 10

Microsoft isn't going away anytime soon. Last year, the company reported $86 billion in sales, with Windows running on 95 percent of the world's computers. But PC sales continue to decline as people turn instead to tablets and smartphones, according to research firm IDC. And that's bad news for a company that makes most of its money selling work-oriented software.

It doesn't help that businesses increasingly rely on multiple devices, most of which don't run Windows.

Microsoft has a paltry 2.8 percent share of the mobile software market, which is dominated by Google's Android OS and by Apple's iOS software for the iPhone and iPad. That's a massive problem considering that 2 billion people -- or more than a quarter of the world's population -- will have a smartphone by the end of 2016, according to eMarketer.

It's also a big part of the reason that, when it comes to creating new apps, mobile and otherwise, developers rarely give Microsoft a second thought.

"They're so far behind on phones that they would really have to come up with something near an act of God even to turn it around," said Rob Enderle, an industry analyst with the Enderle Group.

Windows 10 has the potential to solve some of Microsoft's most pressing problems. "Windows 10 will be a service across an array of devices and will usher in a new area ... where the mobility of the experience, not the device, is paramount," Nadella told investors Thursday after Microsoft announced earnings and said that its profit topped Wall Street's expectations.

What that means is a promise to developers and consumers that Windows 10 will be a single platform to run all their apps on across all their devices. Developers will write to a single code base, allowing them to create a so-called universal app that will work across any device so long as that device runs Windows 10. Those devices can include phones, tablets, PCs, the Xbox One game console, TVs and even the new HoloLens virtual-reality headset.

"There will be one way to write a universal application, one store, one way for apps to be discovered, purchased and updated across all of these devices," Terry Myerson, Microsoft's executive vice president of operating systems, said at the September unveiling of Windows 10.

At Build, Microsoft is expected to talk about how that will work.

Even with that promise, there's a Catch-22. Windows 10 can't succeed if it runs on phones almost no one buys, powers tablets only some people use and is only installed on newer PCs -- most owners haven't upgraded their operating systems in almost six years.

"It doesn't matter how easy it is to develop for a platform if you can't sell a product because there are no users," Enderle said. Microsoft has "to convince these guys if they develop for the platform that they'll get compensated."

To give the software a push, Microsoft is making upgrades to Windows 10 easier on the wallet. For the first time, Microsoft is giving Windows away for free to users running Windows 7 or later versions. It's also offering its Office suite of apps free of charge on competitors' devices, like Apple's iPhone and iPad, in the hope those apps will prompt users to return to Windows products.

Microsoft's ultimate goal is to get consumers and businesses to subscribe to its cloud offerings, like the Office 365 subscription service. More software makers now view annual subscriptions as the gift that keeps on giving.

The company's cloud businesses are growing fast, too. Growth in that division helped send Microsoft's stock up more than 10 percent last Friday after its earnings report.