VMware Enhanced VMotion Compatibility (EVC)

http://www.vmware.com/files/pdf/vmotion_info_guide.pdf

VMware Enhanced VMotion Compatibility (EVC)—available in VMware Infrastructure 3 beginning with
version 3.5 Update 2—facilitates VMotion between different CPU generations, taking advantage of Intel Flex
Migration and AMD‐V Extended Migration technologies. When enabled for a cluster, EVC ensures that all
CPUs within the cluster are VMotion compatible. CPUs starting with Intel 45nm Core 2 (Penryn) and AMD
Second Generation Opteron (revision E or F) incorporate FlexMigration and Extended Migration technologies,
respectively.
The EVC feature allows the virtualization layer to mask or hide certain features by modifying the semantics
of the CPUID instruction and hides certain CPUID feature bits, even from nonprivileged code. For example,
with support from hardware, the virtualization layer modifies the semantics of the CPUID instruction to mask
or hide the SSE4.1 feature from any code (privileged or nonprivileged) to make CPUs differing in this feature
compatible for VMotion. Specifics on CPU compatibility with the Enhanced VMotion Compatibility feature
are available in the Basic System Administration guide for each ESX release starting with version 3.5 Update 2.