Long after Bill Gates's departure from full-time work at Microsoft, his intensive interrogation of subordinates during frequent product reviews will remain a telling collective memory of the man.

In a company whose culture was founded on intellectual ambition, there has been no more stringent challenge than going toe-to-toe with Mr Gates.

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"They say a dog can smell fear - Gates could tell where the weakness in your proposal was and go straight for it," says Michael Cherry, a former Microsoft programme manager who was among those to come up against the software industry's Grand Master.

Even without his founder's status, Mr Gates's legendary intellect - the first attribute on the lips of anyone who has worked with him - gave him an unchallenged position at Microsoft.

He magnified that impact on the management and culture of the company with so-called "Think Weeks," annual periods when he would retreat to ponder stacks of papers from Microsoft employees on the future of the technology industry. Microsoft's staff may have swelled to more than 80,000, and most may never have had the chance to go up against the iconic founder, but the creation-myth that surrounds Mr Gates will die hard.

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That makes the move to a post-Gates era one of the most challenging successions any big US company has faced, even if the subtle effects on Microsoft's culture will be largely invisible to the outside world.

Microsoft has worked long and hard to prepare for this moment. Mr Gates's gradual ceding of power began at the start of the decade when, drained by trying to run all aspects of the company as it fought spreading antitrust cases in the US and Europe, he handed the chief executive duties to Steve Ballmer.

More recently, Mr Ballmer has brought in a new layer of executives to try to get to grips with the complexity of managing the spreading software conglomerate and free himself to take a longer-term perspective.

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Kevin Turner, a former Wal-Mart executive, says he spent eight hours in a Denver airport meeting room with Mr Ballmer four years ago hashing out how Microsoft would run after Mr Gates's departure.

Mr Turner eventually joined Microsoft as chief operating officer.

Mr Gates finally disclosed his pending departure two years ago, using that occasion to step back from his official role in charge of the company's technology strategy and development efforts. Since then he has progressively distanced himself from day-to-day management, according to Microsoft executives.

Even with all that preparation, Microsoft had to accept that on one level Mr Gates was simply irreplaceable, says Craig Mundie, who has taken over as the company's chief long-term technology strategist.

"You could go write a big ad in the newspaper and say, hey, you know, billionaire genius, please apply here, but wouldn't really find any takers or people who could step into that," he says. He and others concede that Gates's status won't be replicated.

Building a broader senior management team and bringing on Ray Ozzie and Mr Mundie are part of Microsoft's response.

Mr Ballmer, a long-time student of management practice and theory beyond the technology world, says he pulled out an old book from his college days by the German economist Max Weber for clues about how to handle the passing of a charismatic leader.

"The important thing is to point forward and keep people pointed forward," he says.

Mr Turner says that two years ago he set about trying to enshrine some of the business principles that Mr Gates lived by into more objective management processes.

"It's those things that you basically galvanise and institutionalise in the company," he says.

Other aspects of Gates's leadership have also been institutionalised.

Kevin Johnson, head of the Windows and internet businesses, says for the past two years each product team has had to produce a set of formal "quests", or long-term aspirations.

"We've basically operationalised a lot of the things that Bill does," he says.

In spite of all the planning, however, there is no hiding the significance of the transition.

"His technology vision was always incredibly important to the company," says Nathan Myhrvold, a former Microsoft chief technology officer.

"They may feel the loss when they need to make a big, bold bet that lesser men would shrink from."