Before vCenter Server allows migration of running or suspended VM from one host to another, it performs a number of compatibility checks to make sure that this virtual machine will be able to resume or keep running on the new host.

One of the requirements is CPU compatibility, that is, the processor on the target host should be able to provide the same set of features to the VM after migration. This CPU feature set is determined based on the following items:

The reason for the last requirement is that when a virtual machine is booting up, operating systems perform a check of the CPU type with the CPUID instruction. The response tells the OS which features and instructions are available with the current CPU. The OS in turn tells applications which functionality is available...