\[Editor's Note: In response to Michael Otey’s article, "Virtualization Shootout, Part 2," Microsoft submitted the following letter to the editor stating the company’s position on the performance data.\]

 According to the development schedule specified in “Virtualization Shootout, Part 2” in the July 2008 issue of Windows IT Pro, Microsoft’s Hyper-V was tested using pre-released beta code. The performance data in the review may not represent an apples to apples comparison because all of the performance optimization occurs at the very end of development cycle.

Microsoft customers and partners are seeing great cost savings and performance results within their datacenters. Most recently, QLogic  published a benchmark for I/O throughput for storage devices going through Windows Server 2008 Hyper-V. At 180,000 I/Os per second on a system running Hyper-V, virtual machine connections are just 10 percent shy of native performance. This benchmark demonstrates Hyper-V’s ability to bring the advantages of virtualization to the most demanding datacenter. For more information on installing and testing Hyper-V, please check out the tuning guide.

—Microsoft