use to transfer input data and results between web browsers and other clients and server-side scripts perhaps more useful way to understand cgithoughis in terms of the interaction it implies most people take this interaction for granted when browsing the web and pressing buttons in web pagesbut lot is going on behind the scenes of every transaction on the web from the perspective of userit' fairly familiar and simple processsubmission when you visit website to searchpurchase productor submit information onlineyou generally fill in form in your web browserpress button to submit your informationand begin waiting for reply response assuming all is well with both your internet connection and the computer you are contactingyou eventually get reply in the form of new web page it may be simple acknowledgment ( "thanks for your order"or new form that must be filled out and submitted again andbelieve it or notthat simple model is what makes most of the web hum but internallyit' bit more complex in facta subtle client/server socket-based architecture is at work--your web browser running on your computer is the clientand the computer you contact over the web is the server let' examine the interaction scenario againwith all the gory details that users usually never seesubmission when you fill out form page in web browser and press submission buttonbehind the scenes your web browser sends your information across the internet to the server machine specified as its receiver the server machine is usually remote computer that lives somewhere else in both cyberspace and reality it is named in the url accessed--the internet address string that appears at the top of your browser the target server and file can be named in url you type explicitlybut more typically they are specified in the html that defines the submission page itself--either in hyperlink or in the "actiontag of the input form' html however the server is specifiedthe browser running on your computer ultimately sends your information to the server as bytes over socketusing techniques we saw in the last three on the server machinea program called an http server runs perpetuallylistening on socket for incoming connection requests and data from browsers and other clientsusually on port number processing when your information shows up at the server machinethe http server program notices it first and decides how to handle the request if the requested url names simple web page ( url ending in html)the http server opens the named html file on the server machine and sends its text back to the browser over what' server-side cgi script