Let us star with the basic function of the web server. The function of the web server is straight, that means following a request from the browser, the server starts hunting for the information or document. When it finds one it immediately provides to the user. But to cope the demand of the customers the functionality of the server need to be extended. Now the back-end application has become has become quite common, which is applied via the CGI program. The reason of back-end application of server has become necessary for various reasons. For trivial information one can not devote plenty of time. Therefore organizations go for building data base and back-end application of the server so that people of a particular gather their individual information.

Here the role of the script is immense. The script can change all the incoming or out going data or information. Sitting between the script and server, the CGI plays a vital role and provides a key service. Now let us discuss how the CGI works with the server.  For the back-end application CGI needs to be connected with the data-stream from the server. At the request of the browser, the URL starts work and the server begins to load and run the program. A data-stream is usually sent back to the server, which in turn is sent to the client. Some time request is made to run a script, in such a situation URL specifies a subdirectory from where the executables are found. This has been done for the integrity and security of the system. Here we should know about the communication mechanism that helps to transfer the data or the information. There are four mechanisms of communication that are used for the purpose of transferring data to the script. Such mechanisms are variables of environment, command line application, standard input application and standard output application.