Microsoft CEO Satya Nadella. Manish Swarup/AP When Satya Nadella took over as CEO of Microsoft in February 2014, he brought a brand-new playbook to the company. Instead of focusing exclusively on Windows, his Microsoft would take a "cloud-first, mobile-first" stance.

Just over three years later, things are looking good. Microsoft stock is hitting all-time highs, as Wall Street responds favorably to the strong and continued growth of the Office 365 subscription productivity suite, and the Microsoft Azure cloud computing service — the poster children for Nadella's post-Windows approach.

And yet, when Microsoft announces its quarterly earnings results on Thursday after the bell, it still has a lot to prove, to Wall Street and to the world. Because while Nadella's vision has led to a reinvigorated Microsoft, the biggest question remains: Will Nadella's big bets on the cloud and mobile grow fast enough to offset its fading old businesses?

If Microsoft can't show clearly that the answer is "yes," Wall Street could lose faith in Nadella's master plan.

Here are the major things to look out for when Microsoft announces earnings on Thursday:

In other words, investors are on board with Nadella's vision for a world where Microsoft weathers the shrinking PC market by dominating the worlds of the cloud and business software.

But these older businesses still account for a tremendous chunk of Microsoft's revenue. And while the cloud is growing fast, investors will be looking for signs that this growth will translate into a big enough, high-margin business to offset that shrinkage.

We'll be covering Microsoft's earnings live, so make sure to come back Thursday after the bell. Wall Street analysts are expecting Microsoft to report earnings of $0.70 a share on revenue of $23.62 billion.