Bill Gates will step down from his day-to-day role at Microsoft Corp. in July 2008, three decades after founding the software maker that now controls almost 95 percent of the world's personal computers.

Gates, 50, will remain chairman after that. Ray Ozzie will immediately assume Gates's job of chief software architect and Craig Mundie will become chief research and strategy officer, the Redmond, Washington-based company said today in a statement.

Chief Executive Officer Steve Ballmer will remain in his role, charged with reviving sales growth and a stock price that has tumbled 16 percent this year.

``This is the beginning of a major change of the guard at Microsoft,'' said Rob Enderle at the Enderle Group in San Jose, California. ``This probably heralds one of the biggest changes in the firm that it's ever experienced.''

The appointments of Ozzie and Mundie signal Gates is reaching more broadly through the management team in his efforts to map out future strategy. Microsoft has struggled to catch up to Google Inc., the world's largest search engine, and has been weighed down by delays in releasing the company's latest Windows update.

Mundie, 56, started at Microsoft in 1992 to run the division responsible for consumer products and services outside of personal computers. Mundie, who has described himself as Microsoft's ``Secretary of State,'' leads negotiations on intellectual property and piracy issues.

Ozzie, 50, is the founder of Lotus Notes and has been with Microsoft for a little over a year, joining when Microsoft bought his Groove Networks Inc.