What's in the box? IBM's Power5 architecture…

Also coming with Power5 is simultaneous multithreading (SMT), an ability for a single processor to handle some of the work of two. The technology gives about a 30 per cent performance boost, IBM said, but requires the new AIX version 5.3.

One of the major new features of the Power5 servers is 'micro-partitioning', the ability to run as many as 10 operating systems on each processor. The feature makes it easier to replace multiple systems with a single centrally managed machine, especially because management software can automatically reallocate resources as work loads shift.

The new partitioning addresses a major weakness of the Power4 generation: the requirement that each partition have its own adapters for networking and storage systems.

"When we looked at Power4, at a certain point, it became cost-prohibitive to slice it up into logical partitions," said Robert Gamso, senior principal systems architect at appliance maker Whirlpool, a long-time IBM Unix server customer with about 100 systems.

IBM will improve flexibility of portioning will improve when the Power5+ in 2005, when one machine will be able to move a partition quickly to another. The feature is available today, but only using a relatively slow networked storage system. With the Power5+ systems it will happen "in a matter of a few seconds" using conventional Ethernet networking, Arimilli said.

A new Linux priority with Power5 meant a change to the IBM's typical approach of adapting the operating system to the processor. With Linux, the influence went the other direction after IBM found programmers unwilling to relinquish Linux's general-purpose but sometimes slower design, Arimilli said.

Linux led to about 20 additions to the Power5 design in areas such as how the chip addresses memory and locks computing resources that are in use, Arimilli said. The changes mean that Linux runs about 90 to 95 per cent the speed of AIX instead of 80 per cent, Arimilli said - though AIX gets a much smaller boost from the hardware changes as well.

"AIX is still superior but as years go by, that gap will close," Arimilli said. And for now: "Linux on Power5 will have much better performance than Linux on other architectures."

Right now, Linux isn't well enough supported by software companies and others to make its worthwhile on Whirlpool's Power servers, though the company does use it on Intel-based systems, Gamso said. That could change: "Once the rest of the market catches up and all the ISVs [independent software vendors] are there, then it's viable," he said.

"Everyone has been on the defensive about a resurgent IBM for some years now," Illuminata's Eunice said but competitors are fighting back. Sun is using a three-pronged chip strategy, while HP argues it will benefit from Intel's Itanium chips for higher-end servers.

Sun's first prong is a partnership with Fujitsu, which is bringing a dose of mainframe expertise to its Sparc64 VI processor. Second is 'two-chip multithreading' designs that can run several instruction sequences simultaneously, midrange 'Niagara' and higher-end 'Rock'. Third is pushing its Solaris version of Unix for Advanced Micro Devices' Opteron processors, newer members of the x86 processors such as Intel's Pentium and Xeon.

Sun has been trying to sell large quantities of servers to preserve its customer base, even if it meant heavy discounts, but that emphasis is changing, said chief competitive officer Larry Singer. "The focus of the company is shifting very much to revenue growth and profitability," he said.

Sun also has an answer to micro-partitioning: N1 Grid Containers, a feature due to arrive by year-end in Solaris 10. These containers make a single version of the operating system appear to have multiple independent instances, and the technology works on x86 chips as well as Sparc chips from Sun and Fujitsu.

Don Jenkins, vice president of marketing for HP's Business Critical Server group, sees several Power5 problems. "The most difficult issue for Power5 is the fact it's proprietary and doesn't run Windows and is an inadequate Linux platform," he said. In addition, a customer buying Itanium servers can get them from multiple companies, whereas Power5 comes only from IBM.

"Proprietary" and "open" are relative terms, though. Itanium systems are available from several server makers but the chip is only available from Intel. At the same time, Power servers come only from IBM but many other companies sell variants of the Power chip for various other segments of the computing market.

And while HP currently can't split subdivide a processor so it can run several operating systems, that feature is coming, Jenkins said. "We are close to bringing out sub-CPU partitioning capability as well," he said.

Two factors likely will mean Itanium systems ultimately will outship Power servers, said Insight64 analyst Nathan Brookwood. The main reason: "Itanium systems can address not only the proprietary Unix market but also the Windows market," he said. The other factor: "If you want a Power system, you're going to buy it from IBM. If you want an Itanium system, you can buy it from HP, NEC, Fujitsu, Hitachi and others."

HP and Intel argued that Itanium would bring a radical new design to last 20 years - far beyond the RISC (reduced instruction set computing) chips such as IBM's Power and Sun's UltraSparc. But so far, that advantage hasn't shown up, Eunice said. "Nothing I have seen indicates the Power architecture is running out of steam."

Stephen Shankland writes for CNET News.com.