he evidence is now overwhelming that Linux, once a symbol of software's counterculture, has become a mainstream technology.

The Linux World conference that begins in New York tomorrow promises to be a staid, corporate affair. The speakers' list is filled with corporate technology people who will be there to discuss the dollars-and-cents rationale for Linux, an operating system that is distributed free and developed according to open-source principles, in which programmers donate their labor to debug and modify the software cooperatively.

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Such speakers will hardly be the visionaries and philosophers of the open-source software movement who were the stars of Linux gatherings of a few years ago.

These days, executives at companies that have adopted Linux speak in pragmatic terms of the benefits of saving money and gaining flexibility.

Even Microsoft has quietly decided to change its tactics this year. No longer will its executives make speeches against what Microsoft regards as the evils of free software and its inherent agenda of denying intellectual property rights.

"We still have those concerns, but you're not going to hear us talking much in public forums about them," said Peter Houston, a strategy executive at Microsoft. "In 2003, we're going to emphasize the business benefits of our software — the value for money, the competitive advantage and the safety of investment for customers from buying Microsoft software."

Microsoft, it seems, is acknowledging that Linux has become a fixture on the competitive landscape, not something that corporate customers can be persuaded to avoid.

To date, Linux has thrived in some sizable niches of the market for operating systems on server computers, the data-serving machines that act as the hubs of computer networks. Linux is widely used on machines that send Web pages to desktop personal computers and for high-performance computing tasks like scientific research, Hollywood special effects and analyses of risk and trading patterns on Wall Street.

But the real issue is how far Linux can extend its reach into everyday corporate computing in all kinds of industries. By 2005, it should be "a mainstream choice," along with Microsoft's Windows and commercial versions of Unix, as a server operating system in most industries, said Dan Kusnetzky, an analyst at IDC, a research firm.

Linux is typically cast as the enemy of Windows, as the populist challenger to Microsoft and the company's drive to extend its monopoly on the PC desktop into the lucrative business of corporate computing. It is true that Linux and open-source software in general pose a threat to Microsoft, the dominant software maker.

Still, the rise of Linux is a more imminent threat to the commercial versions of Unix. Linux is the open-source offspring of Unix, an operating system developed at Bell Laboratories in the late 1960's and early 70's. The leading commercial versions of Unix today are made by Sun Microsystems, I.B.M. and Hewlett-Packard. The Unix flavors run on costly, specialized hardware, while Linux was designed to run on low-cost hardware from the PC industry powered by Intel microprocessors or Intel-compatible chips. And software applications that run on Unix can be moved over fairly easily to Linux.

I.B.M. and Hewlett-Packard are placing big bets on Linux, and both are on a path to phase out their proprietary Unix businesses eventually. Companies like I.B.M., Hewlett-Packard, Red Hat, SuSE Linux, Linuxcare and others make money by supplying hardware, technical support, services or software for Linux systems.

Sun Microsystems, however, is deeply dependent on its homegrown Unix business — on large, powerful and expensive machines running its Solaris operating system.

E*Trade, the online broker and bank, has made a significant shift to Linux over the last year. E*Trade began looking in early 2001 at the potential savings from moving to Linux on Intel-based servers, but it seemed risky, according to Joshua S. Levine, the chief technology officer.

But by the end of 2001, when it became clear that I.B.M. and Hewlett-Packard were really investing in Linux, supporting it with hardware, software and services, Mr. Levine decided to make the move. Last year, the company bought 160 Intel-based servers and converted about two-thirds of its data center to Linux, replacing Unix systems, mostly from Sun Microsystems.

Last year, Mr. Levine says, the move saved E*Trade about $13 million in data center expenses, including maintenance, depreciation and software licensing fees. And the reduced hardware costs, especially after the replacement is complete, proved irresistible. "I'm replacing $200,000 Unix machines with $4,000 Intel servers," Mr. Levine said.

The one thing not being shifted over to Linux machines is the E*Trade databases of customer and trading information. "That is the riskiest thing to do," he said.

Mr. Levine, a 25-year veteran of the corporate computing field, said of Linux: "It's just an operating system, and a minimalist one at that. But Linux unshackles us from a proprietary world. It allows me to manage computer hardware manufacturers like I've never been able to manage them."

Still, rapid conversions to Linux are the exception. That is especially the case at large companies with corps of in-house programmers accustomed to writing programs for other operating systems. And changing technologies can be risky and disruptive.

J. P. Morgan Chase began experimenting last year with using clusters of Linux machines as a high-performance computing environment for conducting risk analyses on vast amounts of market data. Such work is similar in its calculation requirements to scientific research, where Linux has been used for years.

The bank is looking at using Linux-based systems for new applications and when hardware has to be replaced. The pilot projects have gone well, and Linux is now being used for some high-performance applications. "It's real, but it's in the early stages," said John Curcio, vice president for distributed computing.

Earlier this month, Goldman, Sachs issued a lengthy report titled, "Fear the Penguin," a reference to the Linux mascot. "Linux-on-Intel appears likely to emerge as the dominant platform in corporate data centers," the report predicted.

"All of Unix is more at risk than Microsoft's Windows in the next few years," said Thomas Berquist, a Goldman, Sachs analyst and a co-author of the study. "But what is really at risk is the concept of a proprietary operating system. And that has to affect Microsoft."