Mr. Schmidt and Mr. Jobs have their roots in Silicon Valley’s second generation, the engineers and innovators who came after the early era of semiconductor pioneering. Their acquaintance dates from the early 1990’s, when Mr. Schmidt, heading software at Sun, approached Mr. Jobs, then running Next Computer, about technical cooperation between the companies.

While Mr. Schmidt’s credentials include a Ph.D. in computer science from the University of California, Berkeley, his early outlook on the industry was shaped when he worked at the Palo Alto Research Center, the legendary Xerox outpost known as PARC, where the first personal computers and modern networks were created in the 1970’s.

In contrast, Mr. Jobs, a college dropout, started out as a brash hobbyist who in the mid-70’s foresaw a market for the cobbled-together computer that his friend Stephen Wozniak had built to show off at the Homebrew Computer Club in Palo Alto. The result was Apple, which they founded in 1977. PARC was also a touchstone for Mr. Jobs, whose visit there in the late 70’s exposed him to the graphical user interface and the computer mouse, two concepts he eventually brought to market with the Lisa and then the Macintosh.

Both men experienced long periods of relative adversity outside of the limelight of computing. Mr. Jobs was forced out of Apple in 1985 by his handpicked chief executive, John Sculley. He then founded Next, which he ran without great success until he sold it to Apple in 1996 and rejoined the Apple fold.

Mr. Schmidt left his position at Sun Microsystems in 1997 to take over as chief executive at Novell, a network computing pioneer that, like Apple, had been a victim of Microsoft’s rise to dominance in desktop computing. After four years of trying to turn the struggling company around, he left to become chief executive at Google, where his experience was meant to offer balance to the two young founders, Sergey Brin and Larry Page.

Now Mr. Schmidt will bring his experience into play at Apple, in part helping Mr. Jobs add to the independence of his board while the company investigates possible irregularities in stock option grants to Mr. Jobs and other Apple executives.

Executives who know the two men say they have not been close in the past, but are part of a tightly knit fraternity that draws their companies together at the executive level. Former Vice President Al Gore is a special adviser to Google and also holds a seat on Apple’s board. Another link between the companies is William V. Campbell, chairman of Intuit, the financial software company whose Quicken and TurboTax products have prevailed against Microsoft’s challenge.