As well as picking the chips and operating systems they want, buyers of volume servers will next year have to choose between I/O architectures.

As a result, IT managers will have to make some tough decisions, taking into account backwards compatibility, new capabilities and cost.

AMD's 64bit Opteron processor is set to ship on 22 April. For volume server buyers, the choice of processors will have important implications. They will have to decide whether to stay with 32bit operating systems or exploit the power of Opteron and Intel's Itanium 2 with a 64bit version of Linux or the forthcoming 64bit version of Windows Server 2003.

Buyers must also choose between PCI-X and PCI Express bus architectures. Intel is pushing PCI Express - a faster, serial version of PCI that does not offer backwards compatibility - as the bus of choice for servers in the second half of next year.

However, some server makers plan to stay with a 2.0 update to the PCI-X bus standard that is widely deployed on servers today. PCI-X is a faster version of PCI that accepts older network, graphics and other peripheral cards.

An Intel spokesman said: "We expect quick adoption of PCI Express in servers and desktops next year. Most of our chipsets will have PCI Express support."

Dell plans to move directly from PCI-X to PCI Express next year. However, other server makers will not be so swift.

HP, the biggest seller of Intel-based servers in the UK, is unlikely to adopt PCI Express next year, instead plumping for PCI-X and a chipset from ServerWorks, the Broadcom subsidiary that also supports AMD chips.

"We're going to continue to support PCI-X in 2004," said Phil McLean, HP industry-standard product marketing manager.

"Customers invested heavily in NICs and Raid controllers and this gives them investment protection for several years. We're evaluating PCI Express but at the moment there are no [product] plans."

ServerWorks has predicted that PCI Express will not be successful at first because, it said, PCI Express is not significantly better than PCI-X.

Another major server maker, Fujitsu Siemens, uses PCI-X in its current Primergy line and is also wary of commiting itself to PCI Express.

"PCI Express is an interesting technology we consider for future deployment," said a spokesperson. "The big challenge is the availability of supported controllers and the compatibility with PCI-X cards."