The allegation is part of a critical portrait in the book of Mr. Gates, with whom Mr. Allen formed a friendship in grade school that evolved into one of the iconic partnerships of American business. The book, "Idea Man: A Memoir by the Co-founder of Microsoft," is scheduled to go on sale on April 17. A draft of the memoir was viewed by The Wall Street Journal. An excerpt of the book appeared on Vanity Fair's website early Wednesday.

The book gives a revisionist take on some details of Microsoft's history and the relationship between Mr. Gates and his former partner, the two of whom have long been viewed as cordial if not close friends. The book has created a rift between Messrs. Gates and Allen, say people who know both men. In the book's acknowledgments section, Mr. Allen thanks Mr. Gates along with 17 other people for "general and logistical assistance."

The book is "a very balanced portrayal of their relationship," said David Postman, a spokesman for Mr. Allen. "Paul clearly values the input and the ideas and energy of Bill Gates."

"While my recollection of many of these events may differ from Paul's, I value his friendship and the important contributions he made to the world of technology and at Microsoft," Mr. Gates said in a written statement.

Mr. Allen's unflattering account of Mr. Gates in the book is already making waves within the tight circle of early Microsoft alumni, with several people who know both men privately expressing confusion about Mr. Allen's motivations for criticizing his old business partner and questioning the accuracy of Mr. Allen's interpretation of certain events. Mr. Allen, for instance, puts himself in meetings that people familiar with the meetings say he never attended. In one case, Mr. Allen visits Palo Alto, Calif. to help woo a computer scientist who would later become one of the Microsoft's most important programmers. People familiar with the meeting said it was Mr. Gates who made the visit. Mr. Postman said that he isn't aware of any errors in the book.

In the book, Mr. Allen also positions himself as the spark of many of Microsoft's most important ideas, playing down Mr. Gates's role in some cases. Woven throughout the book is a bitterness Mr. Allen expresses for not receiving more credit for his work throughout his career and more shares in Microsoft.

Mr. Allen became one of the world's richest people from the success of Microsoft under Mr. Gates's leadership, with the vast majority of his wealth created in the years after he left the company.

"I am surprised that Paul would have felt that it helps his legacy to express dissatisfaction with the share of Microsoft he received," said Carl Stork, who joined Microsoft in 1981 as a technical assistant to Mr. Gates and worked there for two decades. "While all of us considered Paul a friend and valued his contribution, there is no question that Bill had a far larger impact on the growth and success of Microsoft than did Paul."

Much of the book focuses on the philanthropic and entrepreneurial efforts of Mr. Allen since he left Microsoft as an officer in the early 1980s. His early stake in the company created one of the world's greatest fortunes—he ranks 57th on Forbes magazine's list of billionaires, with an estimated $13 billion fortune—and funded everything from his acquisition of multiple professional sports teams to a successful quest to win a prize for building a reusable spacecraft.

Throughout the history of the technology industry, one co-founder often plays an outsized role in the success of their companies. Mr. Gates, Apple Inc.'s Steve Jobs and Facebook Inc.'s Mark Zuckerberg all saw their co-founders leave before their companies truly took off. Yet the importance of those early partnerships can't be overlooked, said David Yoffie, a professor at Harvard Business School.

"I'm not sure Bill would ever have dropped out of Harvard if it wasn't for Paul," Mr. Yoffie said, referring to Mr. Allen's role in encouraging Mr. Gates to leave college to start Microsoft. "I don't know whether Steve Jobs, without Wozniak, would have ever gotten things together."