Virtualization Capacity Planning

Every virtualization platform has an expected average performance level, which is influenced by several factors that are independent from the chosen hardware -- from optimization of the virtualization engine to the expected load that the virtual machine will have to handle. The number of virtual machines that a single core (or a single CPU, in the case of single core processors) can reasonably support depends on these factors. So, a VMware ESX Server 3.0 and a Microsoft Virtual Server 2005 R2 can have a completely different VM/core ratio even on the same host.