The Web server receives a client request and can perform any number of actions, based on its configuration. If the server is configured to recognize the /gallery.dll portion of the request as a program, it passes information about the request to that program. The way information about the request is passed to the program depends on the type of Web server application:

• If the program is a Common Gateway Interface (CGI) program, the server passes the information contained in the request directly to the CGI program. The server waits while the program executes. When the CGI program exits, it passes the content directly back to the server.
• If the program is a dynamic-link library (DLL), the server loads the DLL (if necessary) and passes the information contained in the request to the DLL as a structure. The server waits while the program executes. When the DLL exits, it passes the content directly back to the server.

In all cases, the program acts on the request of and performs actions specified by the programmer: accessing databases, doing simple table lookups or calculations, constructing or selecting HTML documents, and so on.