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UPDATED: November 11, 2014, at 6:40 p.m.

Harvard’s computer science faculty will grow by 50 percent, or 12 professorships, following a gift from former Microsoft CEO Steven A. Ballmer ’77. Ballmer did not specify the size of the gift.

“I believe in Harvard,” Ballmer said in an interview on Wednesday. “I went to school here and I love the place, and I believe in the power of technology to make a difference.”

Ballmer said that he is “all in” with his support for the faculty expansion, but he declined to specify the value of the donation. Generally, Harvard professorships cost about $5 million to endow, and when prompted as to whether a $60 million gift was an appropriate ballpark figure, Ballmer said that the arithmetic was “pretty good.”

The money, whatever the exact amount, comes with a clear and explicit ambition.

“Right now I think everybody would agree that MIT, Stanford, and Carnegie Mellon are the top places [for computer science],” Ballmer said, adding that some would also include the University of California at Berkeley. “I want Harvard on that list.”

At an event celebrating the gift hosted at the Harvard Innovation Lab Thursday afternoon, Ballmer told a crowd of hundreds of students, administrators, and nearly every member of the Computer Science faculty that the University’s leadership in computer science is “fundamental” to its continued leadership in higher education.

“Steve likes to win,” University Provost Alan M. Garber ’76, who referred to Balmer as an “old friend,” said after the event.

The gift comes during a period of rapid growth for computer science at Harvard. Now the fifth largest undergraduate concentration, computer science has tripled its number of concentrators in the past five years, and Computer Science 50: “Introduction to Computer Science I” stands as the largest class offered at the College this semester with 780 undergraduates.

School of Engineering and Applied Sciences Dean Cherry A. Murray said in 2013 that she expected the School’s faculty to grow roughly 30 percent in coming years as significant portions of the school, including computer science, move to Allston. The computer science division currently counts 24 professors.

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“The field is at an inflection point. We’ve been working on problems that are in a sense about what computers are—how to code computers, how to get them to work well,” said David C. Parkes, area dean for Computer Science. “We’re at a point now where the field is affecting every other field. This is what we mean by the outward-facing aspect of what computer science is.”

Faced with increasing numbers of instructors and concentrators, administrators and faculty members at SEAS have said they are concerned about space availability in the years before the Allston move. Parkes said that space constraints will limit the department’s hiring timeline following the gift.

Still, at the Thursday celebration, Ballmer urged University members to “get moving” in the expansion and called on other donors to join the effort.