There is a newfound sense of optimism toward Microsoft Corporation (NASDAQ:MSFT), and MSFT stock. Microsoft stock touched an all-time high over $65 last week after the company’s fiscal second-quarter earnings report. Yet, earnings haven’t really budged the last five years, as lower PC sales have pressured Microsoft revenue from its legacy Windows and Office products.

Of late, however, Microsoft has shown growth in newer products. The Surface product line and cloud computing, led by the Azure platform, are posting impressive growth rates. And, Surface and Azure are driving much of the optimism that has led MSFT stock to increase nearly 150% in a little over four years.

But, lost in that optimism toward MSFT seems to be the fact that most of Microsoft’s business is relatively unchanged from what it was three to four years ago — if not worse. Windows is a declining platform. There are multiple competitors trying to take down Office, and the cloud shift is cannibalizing some of Microsoft’s SQL Server business.

So, while there’s a reason to see growth coming from Microsoft’s new opportunities, investors in Microsoft stock need to remember that most of the business isn’t nearly as attractive.

Azure and Surface Are Driving Microsoft Stock Higher

There is reason for optimism toward Azure and Surface. The Surface line garners rave reviews, and sales have been strong. Microsoft has an impressive opportunity to drive commercial sales, with the company calling out a major contract with the U.K. Customs Service on its Q2 conference call.

Growth in Azure has been even more impressive. Revenue increased 93% in the second quarter and 104% in the first half of FY17. Microsoft remains well behind Amazon.com, Inc. (NASDAQ:AMZN) and its Amazon Web Services business. But, it has a clear opportunity to get to at least second place in what should be a large, fast-growing end market. That portends years of growth in Azure, a potential driver for MSFT stock.

At the same time, however, Microsoft is a huge company, with trailing twelve-month revenue over $85 billion. And, neither Azure nor Surface represents a significant portion of those overall sales. Microsoft still doesn’t break out Azure sales, but estimates suggest roughly $3 billion in fiscal 2017 — less than 4% of overall revenue.

Per the MSFT 10-K, Surface sales were about $4.2 billion in fiscal 2016, and those sales actually declined 2% year over year in the second quarter. Some of that weakness came from the company’s phasing out of Surface 3, and gross margins have improved. But, Azure and Surface combined are still less than 10% of total revenue. Even adding cloud computing as a whole, the figure barely gets to one-quarter next year, as MSFT is targeting a $20 billion run rate for commercial cloud.

Simple math shows that it’s tough for Microsoft to grow as a whole if only a small portion of revenue is driving that growth. Indeed, that’s been the case this year. Overall revenue grew just 1.2% in the second quarter, and 0.8% for the first half. Excluding phone sales — where Microsoft has all but has exited the business — top-line growth was still under 5% in Q2 and Q1.

Yet MSFT stock now is priced as a growth stock. That might be aggressive.

MSFT Earnings Still Rely on Office and Windows

The problem for MSFT stock is that so much of Microsoft’s business still comes from its better-known products. The More Personal Computing segment generated nearly 50% of first half sales. That includes Windows revenue — which was almost 20% of FY16 sales — along with Xbox, Search, and devices (including Surface).

Surface aside, that’s not a particularly attractive group. Windows revenue seems likely to decline over the long term and has declined in each of the last two fiscal years. Bing has performed well of late, but in part because Microsoft has spent up to attract traffic. The Productivity and Business Processes segment is almost one-third of sales. Prior to Microsoft’s acquisition of LinkedIn Corp, it consisted primarily of Office and Dynamics, MSFT’s CRM solution.

First-half growth has been impressive, growing about 7%, excluding the contribution from LinkedIn. But, that comes after revenue in the segment declined between FY14 and FY16. While Office 365 sales growth looks solid, much of that growth is simply coming from a shift to “on-premise” Office licenses.

Bottom Line on Microsoft Stock

There are two concerns about the long-term growth prospects of Microsoft stock. The first is that some of the recent headline growth in categories such as cloud and office is simply coming from existing products. Some Azure sales are coming from customers switching away from Microsoft SQL Server. Office 365 sales aren’t going to new customers who didn’t have word processing software; rather, most subscribers are former users of disk-based Office products.

The second concern is that so much of the business is stagnant (though bulls might say “stable” instead). That makes overall growth tough: if 20% of the business grows 20%, and the rest is flat or declining, overall growth rates stay in the 4% range.

With MSFT stock steadily appreciated due almost solely to multiple appreciation, rather than earnings growth, investors are clearly expecting sales to pick up. But, it’s important to remember that Azure and Surface won’t be able to drive that acceleration on their own.

As of this writing, Vince Martin did not hold a position in any of the aforementioned securities.