Adding extra processor post-installation versus installing on two - 2008 R2

Question

I have a Windows Server 2003 installation which is getting pretty long in the tooth, so I have decided to install Windows Server 2008 R2 Standard instead. I have verified that the server is capable of running the OS, and everything is set. At the same time, I'm considering installing an extra processor, but the delivery takes a few days.

And now for the question: Is there a difference in the potential performance of an OS if I install it on a server with one processor, and adding an extra one later, versus installing the OS on a server that already has two processors? Should I postpone the installation until both processors are installed? Are there any benefits to this?

I'm thinking maybe the OS will adjust the performance related to the services differently during installation, when only one processor is available, and that the OS is not smart enough to adjust/compensate the same way later when the extra processor is available.

Any thoughts on this?

Answer 1

No, there isn't any difference. Modern OSs counts CPU/cores at boot time and then they manage processes based on the current configuration with no regards of what was the configuration before the change. Also please note that in virtualized environments adding/removing CPU/cores as needed is a well known and diffused practice. Only pay some attention to licensing model, some software/os versions has CPU/cores limitations.