Q. I have a 64-core machine that has hyperthreading, for a total of 128 logical processors. When I enable the Hyper-V role, I only see 64 logical processors. Why?

A. Hyper-V only supports 64 logical processors, so once the Hyper-V role is enabled, only the first 64 logical processors will be exposed. If you're using hyperthreading on your CPUs, this would mean the first 32 physical cores and the 32 hyperthreaded "cores." Because a physical core is preferable to a hyperthreaded one, it's recommended that if you have 64 physical cores, disable hyperthreading. That way, all 64 physical cores will be available to Hyper-V and you'll get the best performance possible.