The personal computer recently celebrated its 30th birthday. Then last week, Silicon Valley staged the PC's funeral.

The eulogy came in the form of three announcements that shook the tech industry. First, Google (GOOG) said it would pay $12.5 billion for Motorola Mobility. Then, Hewlett-Packard (HPQ) said it would explore getting rid of its PC business. In between, Dell warned that PC sales were under pressure, and watched its stock get whacked by 10 percent.

Together, these events tell us two important things. First, we have officially moved from the PC era to the age of mobile computing. And second, a massive upheaval looms for the industry that built Silicon Valley.

The shift from PCs to mobile computing promises to scramble the hierarchy of tech companies, creating new winners and losers, and propelling all sorts of partnerships and deals that seemed unthinkable even just a year ago.

"The reality is that all these companies are going to be going through big changes," said veteran tech analyst Rob Enderle. "Even if they do emerge on top, they might look a lot different than they do today."

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