Stocks posted a mixed finish to the trading week. The Dow Jones Industrial Average (^DJI -1.02%) declined slightly while the broader S&P 500 (^GSPC -0.67%) notched a small gain.

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Source: Yahoo! Finance.

The economy grew at a slower pace than expected over the last three months, according to data released today. GDP rose at a 1.2% annual rate in the second quarter, according to the latest official data, compared to the 2.6% that economists were targeting. Consumer spending was a bright spot in the report, but falling business investments and a surprising drop in inventory levels held growth back.

As for individual stocks, Alphabet (GOOGL -0.28%) (GOOG -0.33%) and Western Digital (WDC 1.51%) made large moves on Friday in response to earnings announcements that they each released before the opening bell. 

Alphabet's $800 day

Google owner Alphabet gained 3% and briefly passed $800 per share for the first time after the search engine giant posted surprisingly strong quarterly results. Like Facebook did earlier this week, Alphabet credited its mobile platform and investments in online video delivery for helping it deliver major operating wins -- and gushing profits.

Revenue rose by 21% in the Google segment as the company generated 30% more paid clicks on its advertisements. The increased volume easily offset the slight decline in per-click revenue that is a consequence of traffic moving away from desktops and toward smartphones. Google's operating income surged higher by 26% to $8.3 billion.

The "Other Bets" segment, which covers a wide range of investments in areas like fiber optic networking and self-driving cars, grew revenue but its operating loss worsened to nearly $1 billion.

Investors had no problem looking past that issue, though, given that Alphabet's overall profitability improved to 35% of sales from 34% a year ago. For a company of this size, even a small change like that makes a big difference: Alphabet's net income soared 21% higher to $4.9 billion.

Western Digital's competitive market

Western Digital was one of the S&P 500's worst daily decliners, dropping 12% following its Q2 earnings announcement. The data storage specialist beat consensus estimates by posting a 10% sales improvement and a 16% decline in non-GAAP earnings. Management said that the recent combination with SanDisk has them optimistic about the increased market potential. "Western Digital now has a broadened portfolio of solutions for the data center, client device, and client solution markets," Chief Operating Officer Mike Cordono told investors in a conference call.

Image source: Getty Images.

Meanwhile, the company is busy cutting costs in its legacy business. It has reduced its factory footprint by 20% while cutting the workforce by 25%. Those cuts weren't enough to protect profit margins from falling as hard drive volume slipped.

Wall Street may have been more spooked by Western Digital's short-term forecast that targets roughly $4.5 billion of revenue next quarter. That outlook reflects the fact that executives are seeing increased pricing pressure from competitors, especially at the lower end of the market. However, the company sees reasons for optimism around demand, including refreshed product cycles on smartphone devices in the autumn and more penetration of solid-state drives into PCs. Yet given the competitive dynamics in the industry and the complicated integration effort under way, Western Digital shareholders should be prepared for bumpy results over the short term.