Sorry, I need a essence difference instead surface difference.

I know that Servlet is running as a thread and CGI often in a process. If not the textbook tell me such thing, how can I know CGI is running in process and Servlet is running in thread?

More concretely, how do we create a process or a thread using Java? If Java can't, what language can? I know you begin a new program often begin a new process. But why? There must be something under the surface.

tks.