The analyst company did a side by side comparison of VMware's vSphere 4, released in May, Citrix's XenServer 5.5, released in June, and Microsoft's , which is due to ship with its Windows Server OS upgrade in October.

Despite several improvements, Hyper-V will still lack three of the 27 features that Burton Group considers requirements for most enterprise applications running in production, Burton Group analyst Richard Jones said at VMworld Tuesday.

Burton Group compiled a list of criteria for running enterprise applications in a virtual environment, including features related to high availability, live migration, memory management, security, networking, storage, licensing and power management.

Just a few months ago, VMware was the that met all of Burton Group's must-have requirements. It to the list in July following its release of XenServer 5.5.

The analyst company admits that its list of features won't be required for all scenarios, but it sees them as a good general guide. It also noted that Microsoft has won some customers for its existing Hyper-V products, especially among smaller businesses and for departmental use.