Q. If I have a virtualization host that has multi-core CPUs and assign a virtual machine (VM) a single processor, does it have access to all of the cores in the processor?

A. This question has come up a number of times recently, so I thought it was worth straightening out. In your virtualization host (VMware or Hyper-V), you assign a number of virtual processors to each VM. Each virtual processor is equivalent to a core on a physical processor. I say equivalent, because your VM doesn't always map to the same physical core—it's just assured a core's worth of performance.

Note that a virtual processor is a core and not a physical CPU. If I assign a VM a single virtual CPU and my physical processor has four cores, the VM can only access one of the cores of the processor. If I assigned the VM four virtual processors, it could access all four physical cores on the processor.

If you have a quad processor box and each processor has four cores, you can't assign a VM four virtual processors and expect it to be able to access all 16 available cores—it would just see four cores. You can confirm this if you look as Task Manager within the VM.

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