From left, Bill Gates, Satya Nadella and Steven A. Ballmer at a Microsoft event on Tuesday. Mr. Nadella is the third chief executive in Microsoft’s almost 40-year history. Microsoft

From left, Bill Gates, Satya Nadella and Steven A. Ballmer at a Microsoft event on Tuesday. Mr. Nadella is the third chief executive in Microsoft’s almost 40-year history. Microsoft

From left, Bill Gates, Satya Nadella and Steven A. Ballmer at a Microsoft event on Tuesday. Mr. Nadella is the third chief executive in Microsoft’s almost 40-year history. Microsoft

From left, Bill Gates, Satya Nadella and Steven A. Ballmer at a Microsoft event on Tuesday. Mr. Nadella is the third chief executive in Microsoft’s almost 40-year history. Microsoft