Virtualization: VMware vs. Microsoft vs. Xen, 2009: Page 2

4) Understand your guest VM licensing needs – and costs.

VMware: B-

Microsoft: A, because of Windows Enterprise licensing quirks

Citrix: B+

Another balancing act is figuring out the costs of the licenses for your guest VMs versus the cost of the hypervisor or physical server pieces that you need to run them.

VMware in particular has one of the most complex licensing and pricing details, although they have taken steps to simplify it over the past couple of years. One of the advantages of going with Microsoft's HyperV running on the Enterprise version of Windows Server 2008 is that you can have unlimited free licenses for your guest Windows VMs, which can add up to a significant savings. Citrix's licensing is a bit easier to understand and price out than VMware's.

Virtual Server product comparison: VMware vs Microsoft vs Xen: 2009