Hi,
in basic, 1 vCPU (which you configure for your VM) is mapped to 1 logical core.
What a logical core is depends on your server.
If you got 2 AMD CPUs with 6 cores each, you got 12 physical cores, which is 12 logical cores.
If you got 2 Intel CPUs with 6 cores each and Hyperthreading enabled, you got 12 physical cores, but 24 logical cores thanks to Hyperthreading.
So your maximum amount of vCPUs you could configure with vSphere 5.5 would be 12 vCPU per VM on said AMD CPUs and 24 vCPUs on Intel.
Now the more VMs you create with more and more vCPUs, more vCPUs run per logical core. A normal ratio you often see in production is 1-5 vCPUs per locigal core. It really depends on your workloads, whats suitable for your environments.
Hope I didn't confuse you even more ![]()
Tim