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Microsoft CEO Steve Ballmer speaks at a Microsoft event in San Francisco, Wednesday, June 26, 2013. Ballmer, who helped build Microsoft into a technology empire and then struggled to prevent it from crumbling under his own leadership, will retire within the next 12 months. The world's biggest software company did not name a successor. Microsoft Corp.'s stock shot up 9 percent in premarket trading following the news.

( (AP Photo/Jeff Chiu, File))

NEW YORK (AP) — Microsoft CEO Steve Ballmer, who took over the helm of the world's largest software company from founder Bill Gates, will retire within the next 12 months.

Microsoft Corp. did not name a successor. The company said it is forming a search committee and Ballmer will stay on until a replacement is found.

Microsoft shares shot up 9 percent in premarket trading following the news.

Ballmer, 57, met Microsoft founder Bill Gates in 1973 while they were living down a dormitory hall from each other at Harvard University. He joined Microsoft in 1980 to bring some business discipline and salesmanship to a company that had just landed a contract to supply an operating system for a personal computer that IBM would release in 1981.

Ballmer, a zealous executive prone to arm-waving and hollering, did the job so well that he would become Gates' sounding board and succeed him as CEO in 2000.

"It's a tad surprising, but every other business head has been rotated out," said BGC Financial analyst Colin Gillis. "They swapped out all their segment heads over the past few years. The only one they haven't changed is the CEO."

Though investors cheered the news on Friday, Gillis cautioned that it could be a "tough 12 months" for the company.

The obvious successor — former Windows head Steven Sinofsky — got booted by Ballmer, he said.

Sinofsky left the company shortly after the launch of Windows 8 last year.