Microsoft CEO Satya Nadella Microsoft Microsoft's cloud business may be growing faster than Amazon's gargantuan $7 billion Amazon Web Services, but it's still not enough to close a $2 billion gap between them, says Barron's.

To back up its argument, Barron's took a deep dive into Microsoft's financials from its last quarterly earnings statement.

For its cloud businesses, including Azure and Office 365, Microsoft only discloses year-over-year growth rates, not total revenue (to former CEO Steve Ballmer's chagrin), but Barron's made some educated guesses.

Just as bad, if not worse than the Amazon competition, Barron's estimates that the Microsoft Azure cloud — which lets customers rent fundamentally unlimited supercomputing resources from Microsoft's data centers on a subscription basis — isn't growing fast enough to offset sinking sales of Microsoft's lucrative Windows Server and other legacy server products.

But there's some good news: Despite a period of cannibalization, revenue from sales of the Office 365 cloud productivity suite to businesses is finally catching up with the boxed Office software.

Here are the takeaways from the Barron's report:

In the most recent quarter, Barron's estimates that Microsoft Azure generated $560 million in revenue, versus Amazon Web Services' $2.466 billion.

Despite Azure's reported 120% growth over the same period in 2015, it's the second quarter in a row where there was a projected $2 billion-ish gap between Microsoft Azure and Amazon Web Services.

Again despite Azure's growth, it only accounts for an estimated 12% of Microsoft's Server Products & Cloud Services revenue, which booked a 6% decline last quarter. With Server Products sinking an estimated $600 million from the last quarter, the $300 million growth in Azure couldn't offset it.

Office 365 commercial revenue was $2.1 billion in the quarter, estimates Barron's, versus $3 billion for boxed Office commercial sales.

As computer manufacturers shift to the newer Windows 10 operating system, Microsoft has seen less turbulence from the shrinking PC market than expected. But as we approach the one-year anniversary of Windows 10, Barron's says, that buffer will dissipate.

Finally, Barron's estimates that revenue in Microsoft's Surface tablet and laptop division grew an estimated $400 million from the last quarter, versus a decline of $292 million in the Windows business. But that may not last forever, as consumers buy fewer PCs overall

Overall, it doesn't paint an especially rosy picture for Microsoft: Those Microsoft Office stats are encouraging, and Microsoft Azure is growing fast. But Amazon Web Services is the one for Microsoft to beat in the cloud market, and this all indicates that it's not gaining ground quickly enough to offset the diminishing demand for its traditional cash-cows.