My first guess from the above was that this returns the number of virtual CPUs that can exist at the same time on the host, either one or several VMs. In fact it returned 16 in my fedora 20 desktop running with KVM, while this is not the real limit of vCPUs. I can define a VM with more than 16 vCPUs (which does not really make sense when I have only two cores, but it looks cool) and  also I can have well over 16 virtual machines running on the host. I looked into the implementation and now I understand that each driver returns different values, but I do not understand the constants. Can you guys give me some hints how should I understand the output of the command?