Specifying number of processors in VM hardware settings = maximum or always?

As you know I can specify for each VM its hardware configuration.

When I go now to the "Hardware" tab then the default for "Processors" is "1".

I have a quad core CPU system and would like to use 2 CPU cores for this VM.

So when I specify 2 ist fine on the current computer.

However I could imagine that I copy/move this VM sometimes to  a single-core CPU system.

What happens then?

Is the "Processors" value only a maximum of CPUs to be used

or is it an ALWAYS use number of cores option?

Matt