The first excerpt from the year’s most eagerly awaited — and carefully guarded — biography will appear in Fortune on Monday.

The magazine has secured exclusive rights to the sections in Walter Isaacson’s Steve Jobs devoted to Jobs’ relationship to Bill Gates.

For nearly three decades the co-founder of Apple (AAPL) and the co-founder of Microsoft (MSFT) were the twin pillars of personal computing — at times fierce competitors, at times key allies.

According to Simon & Schuster, Isaacson conducted more than 40 interviews with Jobs over the past two years — as well as with hundreds of friends, family members, colleagues and competitors, among them Bill Gates.

By the time the two sat down for a joint interview with Walt Mossberg and Kara Swisher at the All Things D conference in 2007, they were, as Jobs recalled, among the oldest men still active in the industry they helped create.

Steve: You know, when Bill and I first met each other and worked together in the early days, generally, we were both the youngest guys in the room, right? Individually or together. I’m about six months older than he is, but roughly the same age. And now when we’re working at our respective companies, I don’t know about you, but I’m the oldest guy in the room most of the time. And that’s why I love being here.

Walt: Happy to oblige. Happy to oblige.

Steve: And, you know, I think of most things in life as either a Bob Dylan or a Beatles song, but there’s that one line in that one Beatles song, “you and I have memories longer than the road that stretches out ahead.” And that’s clearly true here.

Fortune‘s excerpt will be available for purchase Monday on newsstands and on the Fortune iPad app. A snapshot of it will be online early Monday.