Every time the market for PCs doesn't seem like it could get worse, it does.

Worldwide PC shipments saw their biggest drop in nearly two years, market researchers said this week, reaffirming the ascendancy of mobile and the steady demise of the personal computer.

Research outfit Gartner tracked a 9.5 percent decline in shipments in the second quarter of this year compared to the same time a year ago, posting a tally of 68.4 million units. Meanwhile, researchers at IDC, which doesn’t count tablets in its report, calculated an 11.8 percent drop year-over-year to 66.1 million PCs shipped. To put that number into context, Apple said in its most recent earnings report that it had sold 61 million iPhones during the same quarter—and that’s just one smartphone from one (massively popular) company.

Manufacturers saw declines across the board, both in the U.S. and abroad. Lenovo held on to the title of top PC seller in the world with a 20.3 percent share of the market, according to IDC, followed by US manufacturers HP (18.5 percent) and Dell (14.5 percent).

Of all PC makers listed, only Apple saw year-over-year growth of 16.1 percent, IDC said, a jump likely helped by the release of the new MacBook Air and the MacBook Pro in March, and a figure that could climb even higher if Apple’s Retina-screened MacBook is a success. But to put that in perspective, Macs overall accounted for less than 10 percent of Apple's revenue for that quarter. The iPhone? Almost 70 percent.

This Time It's Not Different

The death of the PC is no longer a new story, and there are always plenty of attempts to explain away the trend—to say why it's different this time. Gartner noted that because of the imminent debut of Windows 10, businesses may have opted to wait to upgrade their PCs. And IDC points out the decline might look especially bad this time around because businesses were busy upgrading a year ago after Windows XP finally died.

But whatever the specifics of any given quarter, the trend line is still clear: it's going down. Which points to the same consistent truth: mobile devices have become the dominant computing platform.

Why else would, for instance, Google upend how its search engine works to prioritize mobile-friendly sites? Google knows that to be useful, it needs to work best on the devices people are actually using. Meanwhile, PC-dependent incumbents like Intel—the primary supplier of microprocessors for less-than-mobile devices—has cited weakening demand from businesses for desktop computers and revised its revenue outlook down.

These days, the big players—Google, Amazon, Apple, Microsoft, Facebook—are putting their resources toward optimizing their businesses for mobile. They haven't all cracked the code, but they're trying. In the meantime, PCs have yet to settle into a niche, given their diminished place in tech’s new hierarchy. With mobile, the question is, what else can we do with it? With PCs, the question is, what are they still good for?