Microsoft Corp. (NASDAQ:MSFT) said Eric Rudder will become its chief of research and development as current head Craig Mundie prepares to retire.

Rudder, 46, is currently chief technical strategy officer for the Redmond, Wash., company, the world's top software developer. He'd previously been a VP for software servers and also worked closely with developers.

Mundie, 62, is an electrical engineer with decades of experience designing computers as well as software. He's been with Microsoft since 1992 and was designated to take over many of the design functions Chairman Bill Gates, now 57, left, when he stepped aside from daily operations in 2006.

Mundie will remain an adviser on projects to CEO Steve Ballmer, 56, until he turns 65 in 2014.

With a payroll of 94,000 as of Sept. 30, Microsoft has had a series of senior research people leave to strike out on their own, as well as a number who came to the company via acquisition.

For example, Gates charged another senior research executive, Ray Ozzie, with taking over part of his duties as well. But Ozzie, 57, left in 2010 to start a new company, Cocomo. He'd sold an earlier company, Groove Networks, to Microsoft in 2006.

Gordon Bell, 68, who was one of the designers of the workstation for the venerable Digital Equipment Corp., has been a senior research scientist with Microsoft since 1995.

But Nathan Myrhvold, 53, the founder of Microsoft Research in 1991, left in 2005 to form Intellectual Ventures, a company that invests in patents. It was among a syndicate that last week acquired patents from bankrupt Eastman Kodak Co. (PINK:EKDKQ).

Microsoft reported spending more than $2.64 billion on research and development in its first quarter ended Sept. 30.

Shares of Microsoft fell 19 cents to $26.81 in Wednesday trading.