Microsoft confirmed on Tuesday that a long-standing and influential member of the Windows OS team has left, one of several recent and imminent executive departures that together represent a changing of the guard at the company.

Rob Short, former corporate vice president of the Windows Core Technology group, left the company last month, according to a spokeswoman from Microsoft's public relations firm.

Short had helped develop the Windows OS at Microsoft since joining the company in 1988. He was on the original Windows NT development team, which did some of the early work to optimize Windows for the PC architecture. Most recently, Short and his team were responsible for the design, development and testing of the core components of Windows.

News of Short's departure follows the announcement last week that Jeff Raikes, head of Microsoft's Business Division, will leave the company in September. Raikes is one of the company's top executives, overseeing Office and all of Microsoft's business products. Microsoft has appointed Stephen Elop, a former executive at Juniper Networks, Macromedia and Adobe, to succeed him.

At the same time Microsoft unveiled Raikes' departure, it also said that Bruce Jaffe, corporate vice president of corporate development, will leave at the end of next month. Charles Fitzgerald, Microsoft’s general manager of platform strategy, also plans to leave the company in the next month or so, Microsoft has confirmed.

When Microsoft Chairman and founder Bill Gates leaves his day-to-day activities at Microsoft midyear, he will leave behind an executive staff that looks vastly different from how it did a few years ago -- which may not be such a bad thing, considering the 33-year-old company aims to generate more revenue from newer business models and technologies.

"It is interesting that the company so far seems to have had some successful outside hires [when it's] had a reputation in the past of chewing them up and spitting them out," said Rob Helm, an analyst with Directions on Microsoft.

However, he noted that the departing Raikes was instrumental in transitioning Office beyond a mere set of desktop applications to become a bona fide business collaboration suite. So it hasn't necessarily been the Microsoft long-timers that have prevented the company from evolving beyond its core businesses, Helm said.

"If Microsoft is moving too slowly in the Web-based world it's not necessarily because the old guard is holding it back," he said. "It may be more a matter of the sheer size of the company and the inherent difficulty of turning a ship that big."

Apart from CEO Steve Ballmer and Robbie Bach, president of Microsoft's entertainment and devices division, many of the company's other top executives have joined the company in the past three years. They include the man widely seen as Gates' successor, Chief Architect Ray Ozzie, who joined Microsoft in 2005. Kevin Turner, Microsoft's chief operating officer, and Steve Berkowitz, senior vice president of Microsoft's Online Services Group, also joined the company that year. And Raikes' replacement, Elop, won't start at Microsoft until the end of the month.