XenSource's Crosby, however, argued that firms such as Central Transport are throwbacks. Companies, once they see the increased performance from upgrading to VT-based Linux servers running Xen, will embrace them.

"AMD and Intel have simply out-invented" VMware, Crosby said. "The real ramp-up of virtualization, we believe, is to run Windows with high performance. Why use what is basically a 10-year-old technology?"

At least one analyst believes that the new Intel chips with built-in VT and upcoming AMD Opteron processors will level the playing field. Gordon Haff, an analyst with Nashua, New Hampshire-based Illuminata Inc., said the performance of VMware's flagship ESX Server will be "pretty similar" to Xen by then.

In the long run, analysts say virtualization itself will become a commodity as it gets built into more operating systems. Windows Longhorn Server, for instance, should introduce built-in virtualization by the turn of the decade, said Haff. VMware and its rivals are already moving up the stack and providing tools that manage multiple virtual environments, he said.