By Kevin Kelleher
August 2, 2013

By Kevin Kelleher, contributor

FORTUNE — Even by the typically unpredictable nature of quarterly earnings, the technology sector had more than its share of surprises this month. As tech giant after tech giant lined up to report their earnings this month, most of them fell short of investor and analyst expectations.

Microsoft (MSFT), Google (GOOG), eBay (EBAY), Intel (INTC), and SAP (SAP): Each one disappointed in net income. Others, like IBM (IBM) and Oracle (ORCL) (which posted earnings in late June), met or beat earnings numbers but fell shy of expectations on revenue growth. At best, things are just muddling along for most of the tech world.

It’s not just the broader economy holding tech back. True, the economy is growing slower than expected this year in the U.S. and in the world at large, but that doesn’t explain why big tech disappointed more than other industries. Why, for example, the S&P 500’s info tech sector was such a disappointment on the earnings front, while consumer and financial companies saw much better-than-expected earnings.

The unpleasant truth for tech investors is that a lot of big-cap, low-value stocks are having trouble jumping over the modest bar Wall Street has set for them. Some, like Intel, fell a mere penny short of analysts’ estimates. Others, like Microsoft, fell a more startling 9 cents a share. Still others, like Amazon, posted a net loss of 2 cents a share when Wall Street had been looking for a net profit of 5 cents a share.

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Many of the less-then-spectacular earnings reports came from companies that are longtime leaders of industries that are approaching or already in decline. Notably, the slowdown in demand for PCs took a substantial toll on the earnings of both Microsoft and Intel, long the leading respective makers of software and processors for desktops and laptops.

There were notable bright spots. Even thought it was a blue quarter for the blue chips, investors found a few exceptions to celebrate, positive surprises among the field of disappointments. Yahoo (YHOO) beat estimates by 5 cents a share. Apple (AAPL)‘s earnings came in 15 cents ahead of estimates at $7.47 a share. Most unexpected, Facebook’s (FB) 19 cents a share earnings were 5 cents ahead of the consensus.

All three of those companies are in the midst of turnarounds of different kinds. Yahoo is showing signs of pulling out of a slump that has lasted for years. Despite the earnings beat, the news wasn’t all positive. The company’s revenue declined 7% from the same quarter a year earlier, while the bulk of the profit surprise came from Yahoo’s holdings in Alibaba and Yahoo Japan.

Apple isn’t in so much of a turnaround project as it is a value play. A few years ago, Apple’s price-earnings ratio hovered well above 20. On the day before Apple’s earnings, it dipped briefly below 10. Apple’s earnings this quarter showed it can still extract profits from older offerings while it develops future products that may generate new growth.

Facebook is this quarter’s true comeback kid, showing it can do what many investors have doubted it could ever since its IPO: make money from mobile. Facebook’s mobile users are growing, but so are its mobile revenues: They now make up 41% of Facebook’s total ad revenue. In fact, mobile ad revenue grew 75% from the previous quarter alone.

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During July, a month when the Nasdaq Composite (COMP) rose 7%, Yahoo is up 12%, Apple is up 14%, and Facebook is up 48%. And other big-cap tech names? Google, SAP, and eBay are largely unchanged. Intel is down 4%, and Microsoft is down 8%. IBM is up 2%, and Oracle 5%, both modest while still underperforming the market. Amazon, however, is up 9%.

What can investors learn from this past month? In sifting through the data, it helps to remember that earnings season is as much about perception as it is about performance. You can grow wildly, but if you don’t grow as expected, your stock can get hurt. You can be in a slump, but if you’re proving things are turning around, your stock can rally. Is Apple really so bad off? Maybe not. Is Google really that good? Time will tell.

That said, there are clear long-term trends at work here. Even as innovation is the driver for much of growth in technology, it’s displacing a lot of the revenue and market value alike of an earlier generation of tech companies. So Google is so-so in mobile, while Facebook is growing. Yahoo is blah on its own, while its Asian properties like Alibaba are surging. And if you’re making hardware like PCs, tablets, or smartphones, the best you can hope for right now is to tread water until something better comes along.

Quarterly earnings can be a bumpy ride — a one-time surprise can be meaningful in the short-term — but it always helps to keep an eye on the long term. In the technology sector, Wall Street is making a clear statement: The older companies are weighted down by tradition, while the new is disrupting the old guard out of its profits.

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