Microsoft's Bill Gates may be richer, but when it comes to unvarnished business aggression, no one in the high-tech world can top Larry Ellison, the 58-year-old founder and CEO of Oracle. This is a man cocky enough to fly his own fighter jet, competitive enough to have his minions pilfer Gates' trash, and mean enough to verbally flog his executives in public. He's worth $14 billion, making him the fourth-wealthiest American at last count, and unlike his peers who demur on the subject of money, Ellison isn't afraid to admit that he loves being rich.

So explain this contradiction: Last month Ellison spent an hour in front of 1,000 programmers in San Francisco talking about the merits of free software. That's right. A man who became as rich as Croesus by selling software for thousands of dollars per user told this standing-room-only audience that their practice of sharing code on the Internet for an operating system called Linux and charging nothing for it was a good thing. Indeed, it's such a good thing, he said, that Oracle had just taken 3,800 lines of its own proprietary code, developed over more than a decade, and posted it on the Internet for all the world to see. "We're trying to be a good member of the community," he said.

A charity? A breakdown? No. Ellison was sucking up to this group for a simple reason. Developers of free software, in particular the hundreds of thousands of Linux programmers, are hot commodities these days. Ellison, ever the master salesman, was simply adding his celebrity to their annual gathering, Linux World, and giving them his best pitch.

For those not familiar with its genesis, Linux was brought to life 11 years ago by a Finnish college student named Linus Torvalds, who wanted to use his home PC to write programs that would also run on the university's Sun workstations. Linux was the software code he created to do the job.

Businesspeople have tended to associate Linux with the charlatans of the Internet bubble and the flakes who seem to dominate its over-granolaed, Berkeley commune culture. Why? Because dozens of now-defunct Linux companies went public at the height of the bubble, each with its own plan for persuading customers to pay money for free software. Because the record for an IPO's opening-day gain belongs to VA Linux, which shot up 700%, to $239.25 a share, when it hit the market on Dec. 9, 1999, but now, renamed VA Software, trades for about $1. And because Linux adherents trumpeted the view that free Linux would replace costly Windows on every desktop. They earnestly claimed that a community of programmers who worked on the code free in their spare time, who weren't tied to any production schedule, and who willingly gave up all profit-making rights to their modifications in the name of promoting free software worldwide was going to topple Microsoft. It just seemed too preposterous for words.

It turns out that the Linux doubters were wrong. Today Linux has become the hottest thing in corporate America since e-mail and maybe even Windows itself. Yes, most of the Linux IPOs are out of business or on the verge of going bust. Yes, few really believe Linux will ever replace Windows on the desktop. But on the back end, on servers in data centers rather than PCs on desktops, companies like Boeing, Amazon.com, E*Trade Financial, DreamWorks, Google, and virtually every major Wall Street firm have either finished reconfiguring big chunks of their servers to run Linux or are in the process of doing so. General Motors says it is likely to do the same in a year or so. Even the Chinese and German governments, along with about two dozen other countries, are taking a look at how they can save money by using Linux in their infrastructures.

This conversion is already causing reverberations throughout the high-tech world. For the year ended June 30, the number of servers sold with Linux as the operating system grew 18%, while those sold with Windows grew only 3% and those sold with Unix fell 7%, according to research group IDC. IBM says that contracts for its Linux integration and support services now number around 800, compared with 95 only 15 months ago. And Dell and HP say they will sell 15% to 18% of their servers this year with Linux preinstalled, up from less than 10% last year.

It's still early in the conversion cycle. IDC says servers running Linux represent only 5% of the servers in operation, compared with 27% for Windows and 43% for Unix, the umbrella term for the proprietary operating systems largely in use by IBM, HP, and Sun. And there are still big business applications like Siebel's that don't yet support Linux. But IDC predicts that by 2006, Linux and Windows will have all but replaced Unix as the dominant server operating systems. It forecasts that 26% of servers in operation will be running Linux, 56% will be running Windows, and only 12% will be running Unix.