On DiPetrillo's point that Hyper-V has only been generally available since June 26, Waldman said numerous Microsoft customers were using Hyper-V in production before then through an early adoption program. Most of Microsoft's virtualization market share comes from its pre-existing product, Virtual Server 2005, but Waldman said he expects Hyper-V's market share to continue rising.

DiPetrillo also questioned how IDC counted shipments of Microsoft's Virtual Server 2005, given that it is a free download off Microsoft's Web site. Waldman said the IDC survey only counted new licenses if they were actually put into production.

Waldman denied another assertion by DiPetrillo, who claimed the IDC survey - which is part of the firm's Worldwide Quarterly Server Virtualization Tracker - was sponsored by a "competitor in Redmond" -- i.e. Microsoft.

"The is not a sponsored product. It is available on a subscription basis to all of our clients," Waldman said.

DiPetrillo, in a phone interview, said VMware didn't subscribe to the Server Virtualization Tracker and thus were not given a chance to offer input before numbers were published. "IDC has never contacted VMware for its actual shipment numbers," DiPetrillo said. "Since we didn't subscribe to the Virtualization Tracker we don't get input into it."