Microsoft (NASDAQ:MSFT) is scheduled to report fiscal fourth-quarter earnings after the market close on Tuesday, July 21. Here are three things to watch for in the software giant's results.

The growth of the cloud
One of CEO Satya Nadella's main priorities is to position Microsoft as a primarily cloud- and mobile-based business. Microsoft's cloud business is a particularly promising growth driver, with commercial cloud revenue surging 106% year over year in the third quarter. Strong results in Microsoft's Azure enterprise cloud computing platform and Office 365 cloud-based productivity software suite helped fuel that growth.

The Office franchise is an especially vital aspect of Microsoft's business. While Windows is besieged by the relentless growth of Apple's Mac OS and iOS, a well as Google's Chrome OS and Android, Office remains a dominant force in productivity software, with market share estimates that exceed 90% of all enterprise PCs. And Nadella recently made the bold move to make Office available on iOS- and Android-powered devices, which has resulted in solid gains in mobile users.

Investors will be looking for evidence of continued strength in Microsoft's cloud-based businesses -- including strong net subscriber additions for Office 365 -- as they are expected to drive much of Microsoft's revenue growth in the years ahead.

Surface assault
While Azure and Office 365 are fueling Microsoft's cloud ambitions, the impressive growth of its Surface line of tablets is providing the tech giant with a beachhead into the mobile device arena.

Surface revenue jumped 44% to $713 million in the third quarter, driven by the strong performance of the Surface Pro 3. Marketed as a "tablet that can replace your laptop," the Surface Pro line is an appealing option for enterprise customers that enjoy the portability of a tablet but also require laptop-like computing performance.

Yet continued share gains may be difficult to come by, due to the iPad's strong consumer appeal and Apple's partnership with IBM to further target the enterprise segment. Still, investors are likely to key in to fourth-quarter Surface sales as they watch this battle unfold.

Windows and the health of the PC market
Even as Microsoft transitions to a cloud- and mobile-first enterprise, the importance of its Windows business should not be overlooked. While Microsoft has yet to gain a significant share of the mobile device pie, Windows still powers approximately 90% of global desktop computers. More importantly, Windows produces a tremendous amount of cash flow that Microsoft can then invest in its growth businesses and return to investors in the form of dividends and share repurchases.

In addition, the results of Microsoft's Windows operations also serve as a barometer for the overall PC market. As such, many investors will be looking for clues in Microsoft's fourth-quarter results not only as to the health of Microsoft's highly profitable Windows franchise but also for the health of the global PC market overall.

Joe Tenebruso has no position in any stocks mentioned. The Motley Fool recommends Apple, Google (A shares), and Google (C shares). The Motley Fool owns shares of Apple, Google (A shares), and Google (C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.