When you select a custom configuration, the New Virtual Machine wizard prompts you to specify the number of processors for the virtual machine.

Specifying multiple virtual processors is supported only on host machines that have at least two logical processors. Single-processor hosts that have hyperthreading enabled or dual-core CPUs are considered to have two logical processors. Multiprocessor hosts that have two CPUs are considered to have two logical processors, regardless of whether they are dual-core or have hyperthreading enabled.