And a discussion is what it got.

After this item posted last week, a number of readers commented on whether claims by VMware's Eric Horschman - - that ESX Server 3 beats Hyper-V and XenServer v4 - - were actually on point.

Some commenters criticized Horschman's methodology of using a server with only 4 GB of memory and virtual machines that carried a light work load with Windows Vista.

Stan Kasper wrote:

My experience has been that the memory sharing features in ESX place a heavy burden on performance. In fact, to optimize performance I disable the PSHARE option and do a fixed allocation of memory for each VMWare guest. PS My initialze test on the beta Hyper-V vs ESX for disk performance is that they are about equal, and maybe Hyper-V is a bit faster. But do not read to much into this as benchmarks are rather a finicky science.

Simon Crosby, CTO of Citrix' virtualization efforts, also wrote a response and followed up with a telephone conversation. He argued that to test for a real, enterprise ROI case, the full cost of deploying the solution has to be accounted for - - not just the software.

"If you want to bring up 100 virtualized desktops, or thousands, how much is it going to cost? That's how you do an ROI case."

So Horschman went back and, seeking to respond to his critics, spelled out some of the algebra involved in supporting his argument that VMware outranks the others in ROI.

James O'Neil, on Microsoft's TechNet blog site, took it a few steps further - - outlining a lengthy formula he suggested gets to the ROI case of virtualization.

Excerpt: "The cost of the Microsoft system is CH + CM MHm + CMS +COS

And the VMware one costs CH + CM MHV + CVMW +COS If CMS is zero and the systems cost the same then CM MHm = CM MHV + CVMW"

(Remember the old Chevy Chase-as-Gerald Ford line? "I was told there would be no math.")

So now what? First of all, Hyper-V is in beta - - it's not in manufacturing - - so those results all come with an asterisk on both sides of the equation. Second of all, none of the algebra takes into account the time and cost of a solution provider actually, you know, solving or managing a customer problem. None of these solutions deploy or manage themselves. That will ultimately factor into all the mathematics, too.