The features it still lacks for the enterprise, according to Burton Group, are the ability to prioritize virtual machine restarts; support for a minimum of two virtual CPUs per guest operating system; and the lack of a fault-tolerant management server.

The first can be important because dependencies can exist between virtual machines, so companies may need to start them in a particular order, said Burton Group analyst Chris Wolf. The second translates to a lack of compute power: Microsoft supports more than two virtual CPUs with its newest OSes, but only two with Windows Server 2003, and one for all other operating systems, Wolf said.

On the third point, Microsoft's System Center Virtual Machine Manager can't run on a cluster of servers, Wolf said. "Microsoft will argue that you can put it in a virtual machine and fail the VM over [to another server], but that's not the point; it can't be made fault tolerant," he said.

Nevertheless, the upcoming Hyper-V release has some significant enhancements, including live migration of virtual machines; cluster shared volumes; support for third-party cluster file systems; hardware-assisted memory virtualization, and virtual storage hot-add, Jones said.

The company also does better than Citrix on the list of features Burton Group considers "preferred" but not required. Hyper-V will lack 14 of the 42 preferred features, while XenServer lacks 17 and VMware seven. The picture is similar for "optional" features.