The maximum number of virtual CPUs that you can assign to a virtual machine depends on the hardware version number of the virtual machine, the number of logical CPUs on the host, and the type of guest operating system that is installed on the virtual machine.
Be aware of the following limitations:
A virtual machine cannot have more virtual CPUs than the number of logical cores on the host. The number of logical cores is equal to the number of physical cores if hyperthreading is disabled. The number of logical cores is equal to twice the number of physical cores if hyperthreading is enabled.
Not every guest operating system supports Virtual SMP, and guest operating systems that support this function might support fewer processors than are available on the host. For information about Virtual SMP support, see the VMware Compatibility Guide at http://www.vmware.com/resources/compatibility.
Hyperthreaded hosts might affect virtual machine performance, depending on the workload. The best practice is to test your workload to determine whether to enable or disable hyperthreading on your hosts.