When investment bank Dresdner Kleinwort Wasserstein began making the switch to the Linux computer operating system in 1999, it did so to save money. Then Dresdner discovered a bonus: Linux, the upstart open-source operating system, was not only cheaper -- but also faster. The Unix servers took 17 hours to calculate how much cash the bank needed in reserve to offset its investment risk. The Linux servers made the same calculation in 11 minutes

Already popular as an inexpensive driver of Web pages, e-mail systems and computer servers on the edges of corporate networks, Linux has begun seeping into corporate data centers where serious computing takes place. As it does, it promises to boost information-technology productivity. But it could also discombobulate two of the biggest tech players -- Sun Microsystems, the dominant Unix supplier, and Microsoft, which is pushing for Windows servers, not Linux, to usurp Unix. ''The real horse race, long term, is going to be between Linux and Windows,'' says Bill Claybrook, analyst at Aberdeen Group.

Microsoft paints Linux as a threat to intellectual property rights. Software developers who make their applications Linux-ready risk losing their proprietary products to the public domain, Microsoft warns. From the Sun and Microsoft view, Linux has not proved robust enough to handle computing chores much beyond the edges of corporate networks. ''All the noise and optimism of the early adopters doesn't in any way guarantee Linux will cross into the mainstream,'' says Peter Houston, Microsoft's Windows server products director.