Allen, in a memoir set for release next month, recalls how he first encountered Gates as a "gangly, freckle-faced eighth grader" in the computing lab at Lakeside high school in Seattle.
"You could tell three things about Bill Gates pretty quickly," writes Allen in the book, "Idea Man" (Penguin), excerpts of which were published this week by Vanity Fair. "He was really smart. He was really competitive; he wanted to show you how smart he was."
Gates would ultimately go to Harvard to study math and Allen would join him on the East Coast with an eye toward starting a software company, which, of course, they did.
Allen recounts how Gates once met him and his girlfriend Rita for dinner in Boston. "Did you see that?" Allen recalls Rita saying. "He ate his chicken with a spoon. I have never in my life seen anyone eat chicken with a spoon."
On a more serious note, Allen claims Gates welched on an original agreement to split their interest in the newly formed Microsoft 50-50. Gates wanted to amend it to 64-36 in his favor because he felt he did more work. "I'd been taught that a deal was a deal and your word was your bond. Bill was more flexible," Allen writes.
"There's a range of elasticity in any business deal, a range for what might seem fair, and Bill pushed that range as hard and as far as he could," says Allen, who ultimately relented to Gates' demand.
Gates' supposed overreaching would foreshadow more underhanded scheming, Allen says. Allen claims that Gates and Microsoft's present CEO, Steve Ballmer, tried to reduce the value of his equity in the company by issuing themselves new options shortly after Ballmer came on board in the early Eighties and Allen was diagnosed with Hodgkin's lymphoma.
"I helped start the company and was still an active member of management, though limited by my illness, and now my partner and colleague were scheming to rip me off," Allen writes. Allen ultimately resigned from Microsoft's board in 2000 to start a number of private ventures. Gates remains chairman of the company.
Microsoft officials did not immediately respond to a request for comment.