From DesigningPatterns

General Characteristics

• When a web server receives a request for a CGI script, it will fork and exec the script.
• GET requests communicate parameters via the QUERY_STRING environment variable; for example, http://www.tony.com/index.rb?name=tony&profession=programmer would result in QUERY_STRING=name=tony&profession=programmer.
• Forking a new server instance for each CGI invocation is expensive, so there are some techniques for making this more efficient, including:
  • FastCGI, in which a persistent pool of processes handle CGI requests.
  • Web server plugins, such as mod_perl, mod_php, and mod_ruby.