If this is common please give me that list of vendors.

My new Proliants can hot plug memory, disk controllers, disk drives but definitely not the CPU (offline, yes). vSphere has the capability to hot add vCPUs and memory. As far as I know swapping out CPUs in a running system is still uncommon.

True. I can remember hotswapping durn near every module in a system the early '90s. But then again I was working with large telecom systems designed with massive redundency.