The industry giants remain highly profitable drivers of the economy. Yet the world’s shift to computing on mobile devices is taking a toll, including disappointing earnings reports last week from Google, Microsoft and Intel, in large measure related to revenue from mobile devices. Investors are in suspense over Facebook’s earnings to be disclosed Tuesday, for much the same reason. Yahoo’s new chief, Marissa Mayer, said on Monday that Yahoo had failed to capitalize on mobile and must become a predominantly mobile company.

Demand for Intel chips inside computers — which are much more profitable than those inside smartphones — is plummeting. At Microsoft, sales of software for PCs are sharply declining. At Google, the price that advertisers pay when people click on ads has fallen for a year. This is partly because, while mobile ads are exploding, they cost less than Internet ads; advertisers are still figuring out how to make them most effective.

Since its initial public offering, Facebook has lost half its value on Wall Street under pressure to make more money from mobile devices, now that six of 10 Facebook users log in on their phones.

Making money will now depend on how deftly tech companies can track their users from their desktop computers to the phones in their palms and ultimately to the stores, cinemas and pizzerias where they spend their money. It will also depend on how consumers — and government regulators — will react to having every move monitored.

Facebook is already experimenting with ways to use what it knows about its users to show ads when they are using other mobile apps. Google can link what a logged-in user does on the computer and phone, to show someone a cellphone ad based on what they have searched for on a computer at home, for instance. But just last week, European regulators warned Google to amend its privacy policy that allows it to gather information about people across diverse Google products, from Gmail to YouTube.