Developing Web Applications

CGI Applications

In the past, Web server application programming would usually require developing CGI programs or scripts.

CGI applications are most widely used on UNIX systems to create executable programs that run on the Web server. CGI programs are typically written in the C language, but can also be written in interpreted languages such as Perl. Remote users can start CGI applications on the server simply by requesting a URL containing the name of the CGI application. Arguments following the question mark in the URL are passed to the CGI application as environment strings. The output of a CGI application isn’t much different from a desktop application; HTTP headers and HTML are generated using the basic output functions of the language (for example, printf in C).

CGI applications are easy to write, but scale very poorly on the Windows operating system. Because a separate process is spawned for each client request, hundreds of clients create hundreds of instances of the CGI program, each requiring its own memory space and system resources. This isn’t such a bad thing on UNIX, which is designed to handle multiple processes with very little overhead. However, Microsoft® Windows® 2000, which is optimized for thread management inside a process, expends more system resources when creating and destroying application instances. As a result, ISAPI was developed specifically for IIS 5.0 as a high-performance Windows alternative to CGI.