Microsoft After Gates. (And Bill After Microsoft.)

In some respects, this week won't be terribly different for Bill Gates than the previous 1,712 weeks he has spent working full-time at Microsoft, the company he co-founded as a teenager. The 52-year-old icon has some one-on-one meetings scheduled with a few of his top technical executives. He has some customer meetings. And, as often happens, he'll go to the television studio on Microsoft's Redmond, Wash., campus to tape a few messages for events he won't be able to attend. In addition, he says, "I hope to write a few memos."

But normalcy will be an illusion. Everybody knows that when the week ends, Bill Gates will walk out of his office for the last time as someone on the clock for Microsoft. (On that final day, the routine will be shredded, and the staff has planned some internal commemorative events.) He'll take a break this summer (including a sojourn to the Beijing Olympics), and beginning in September the new focus of his work life will be the Bill & Melinda Gates Foundation, the organization he began with his wife in 2000. With a current $37.3 billion endowment, it's the world's richest philanthropic institution.

Gates leaves at a challenging time for Microsoft, but this is the final step in a painstakingly planned process that began four years ago. It was spring 2004 when the Gateses began discussing the possibility that if Bill increased his role at the foundation—making as big a donation in brainpower as he has in dollars—he could save or improve many lives. Gates formalized the move in June 2006, when Microsoft announced a two-year transition period scheduled to end, well, right now. "I don't know of any retirement that's been as carefully thought through," says Gates.

The paradoxical aspect of this period has been that while Gates has consciously been stepping back in some areas (almost no one reports to him, and he has limited his tech focus to a few key areas like search and the next version of Windows), his passion for the software world is as intense as ever. "Bill comes to every meeting like he's going to be here for the next 10 years," says CEO Steve Ballmer. So no one really knows how much culture shock will set in when Gates leaves the campus this Friday. Though he will remain the chairman of its board of directors—assuring him a huge voice in any big decisions—and plans to spend the equivalent of one day a week on company business, the idea that he won't be there seems unreal. Microsoft without Bill Gates? It does not compute.

"He's not just Bill Gates, he's the Bill Gates," says Ballmer, the guy who will be holding the bag after Gates leaves the building. "If you were to say who are the five most famous guys on the planet today, he'd probably be on that list. He founded the company, he's accumulated this wealth, he's got this foundation, he's got this fame. That's irreplaceable. Also, Bill grew up with every one of the technologies in this company. He's got more capacity to remember things than anybody I've ever known. It's unlikely we'll have anybody again who has that breadth."

Since Gates and his partner Paul Allen invented the PC software industry (they formed Microsoft to write the first program for the very first personal computer, the Altair), one can say that an era is truly ending. On the other hand, critics of Microsoft contend that Gates's departure is anticlimactic—because the company is past its prime. "The Gates era has already ended—this is the coda," says Mitch Kapor, founder of Lotus, the spreadsheet giant humbled by Microsoft in the 1980s. "Today, Google is the defining company in the industry."