Gates, 50, said Thursday he will remain the company's chairman after transferring his daily responsibilities over a two-year period. One of the key people taking on Gates' responsibilities is technology luminary Ray Ozzie, who developed Lotus Notes and came to Microsoft when it acquired his company, Groove Networks Inc., in 2005.

The move will end an era at Microsoft, which Gates founded in 1975 with childhood pal Paul Allen and has been the public face of ever since. Gates said he is stepping back so he can focus more time on his philanthropic foundation, the world's largest.

The Redmond company on Thursday laid out a plan for other high-ranking executives to take on Gates' duties. Gates and Chief Executive Steve Ballmer also noted that recent corporate reorganizations have been designed to move more responsibility to lower-ranking executives, so the company could more quickly make decisions without Gates and Ballmer.

But, in an interview with The Associated Press, Ballmer conceded that there was no way to replace Gates.

"If we think anybody gets to be Bill Gates, I don't think that's a realistic hypothesis," he said.

Gates stressed that, although he was giving up day-to-day responsibilities beginning in July 2008, he would still play a role at the company.

"I'm not leaving Microsoft," he said.

Gates also said he had no plans to give up the distinction of being the company's largest shareholder.

"I'm proud of that," he said.