Q: Why are only 64 logical processors being used on my Hyper-V-enabled Windows Server 2012 server in the parent partition?

A: After Hyper-V is enabled on Windows Server 2012, the scalability of 64 virtual processors per virtual machine (VM) also applies to the root-parent partition, which is also running on top of the hypervisor.

Therefore, looking at Task Manager on the parent will show two numbers: the number of logical processors, which shows the full number of logical processors in the server, and the number of host logical processors, which will show as 64 (see screen shot below). Note that the hypervisor itself will use up to 320 logical processors distributed amongst both the parent and all the VMs on the server.

Hyper-V Log Core 64