This is the day Sun Microsystems has been dreading. Through all the years of Itanium hype, missteps and delays, Sun has touted its message of software compatibility while spreading fear and doubt about Itanium.

Now Itanium is here, and it isn't going away. Over the next several months, at least 20 vendors will introduce Itanium systems. Intel's investment in the Itanium family continues, with six new versions in the works.

Initial benchmarks show Itanium is not the disaster competitors had hoped for. The 800-MHz processor delivers strong performance on many key transaction-processing and scientific applications.

True, the chip is not as good on basic integer applications; the only server-chip vendor that can't beat Itanium's SPECint2000 score is Transmeta. And Itanium's X86 performance is so bad that Intel won't even talk about it.

Overall, Itanium is within the range of high-end server processors. McKinley (Itanium II), which Intel is testing, will double Itanium's performance, making it the lead.

Sun's problem is that Itanium doesn't have to be better-just good enough. Once end users can choose from among dozens of Itanium boxes and four OSes, Sun's single-arrowhead strategy will look pretty paltry.

Itanium's toughest competition comes not from Sun but its own Pentium 4 processor. At 1.7 GHz, the x86 chip delivers better integer performance and more memory bandwidth than Itanium. Intel has delayed its Pentium 4-based Xeon for servers, but once available, that processor should deliver better transaction-processing performance than Itanium.

I expect Itanium to replace Xeon, but not until 2003, when McKinley and its successors open a performance gap over Xeon. The Itanium chips also offer 64-bit addressing and other features Xeon lacks.

Sun continues to cast aspersions on Itanium, but the company has its own credibility problems. Its UltraSparc-3 entered production last fall more than 18 months behind schedule, and Sun still is not shipping the 900-MHz version promised for the end of last year.

Changes in servers never happen fast. But with Itanium now a reality, Intel's dominance is only a matter of time.

Linley Gwennap is the founder and principal analyst of the Linley Group (www.linleygroup.com), a technology analysis firm (Mountain View, Calif.).