A part answer to your question, including scgi.
- What’s the difference between scgi and wsgi?
- Is there a speed difference between WSGI and FCGI?
- How Python web frameworks, WSGI and CGI fit together
CGI vs FCGI
Lazy and not writing it on my own. From the wikipedia: http://en.wikipedia.org/wiki/FastCGI
Instead of creating a new process for each request, FastCGI uses persistent processes to handle such requests. Multiple processes can configured, increasing stability and scalability. Each individual FastCGI process can handle many requests over its lifetime, thereby avoiding the overhead of per-request process creation and termination