HP will confirm today that it is building Opteron-based servers, said sources familiar with the plan.

It is a dramatic turn of events for HP, which had rejected the AMD chip while its main rivals embraced it, as predicted by Techworld a month ago.

Last summer Peter Blackmore, executive VP of HP's enterprise systems group, said the company had no interest in offering the processor. "It would just add a complication that is completely unnecessary," he said.

In taking this step, HP joins IBM, which began shipping Opteron-based servers last year, and Sun, which recently unveiled its own Opteron-based servers. Sun has also entered into a broader agreement with AMD to develop application support for the chip.

HP officials declined to comment in advance of the announcement but, for the last month, marketing officials at Sun and HP have been gearing up with a war of words over the processor. When Sun detailed its Opteron servers earlier this month, HP marketing officials emailed bullet-point criticisms of Sun's strategy to reporters, points that are likely to be thrown back at HP.

For example, HP wrote: "Adopting the Opteron chip demonstrates that Sun was wrong about its proprietary position. It is now desperately back-pedalling on its long-time strategy to offer a platform based on its UltraSPARC chip and sprinting to get on the industry-standard bandwagon."

For their part, Sun marketing officials, anticipating the move by HP toward the Opteron, raised their own series of points. Among them: "Clearly, it signals that HP is finally giving up on Itanium." Sun also believes that the move jeopardises HP/UX because that Unix operating system isn't ported to Opteron.

The processor is gaining ground with users. IBM originally targeted high-performance computing applications with its Opteron offering, but said the chip is getting use outside that space.

A key feature of Opteron is its ability to run 64-bit as well as 32-bit applications. Intel, at its developers conference IDF this month, said it would produce the Nocona Xeon processor, which will also have 64-bit extensions. That chip is due to ship sometime in the second quarter.