The maximum number of virtual CPUs that you can assign to a virtual machine is 256. The number of virtual CPUs depends on 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 or two times that number if hyperthreading is enabled.
If a running virtual machine has 128 virtual CPUs or less, you cannot use hot adding to further increase the number of virtual CPUs. To change the number of virtual CPUs beyond that limit, you must first power off the virtual machine. By contrast, if a running virtual machine already has more than 128 virtual CPUs, you can use hot adding to further increase the number of virtual CPUs to up to 256.
The maximum number of virtual CPU sockets that a virtual machine can have is 128. If you want to configure a virtual machine with more than 128 virtual CPUs, you must use multicore virtual CPUs.
Not every guest operating system supports Virtual SMP, and guest operating systems that support this functionality 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.