ever wondered how web pages reach your screen?

If you've ever wondered what happens when you call up a web page, what follows represents a simple — some would say simplistic — guide to what’s going on ‘under-the-bonnet’. Nevertheless, here goes…

Say you click on a link, or type a URL such as www.abcon.net into your browser’s address bar (normally your browser will automatically add the prefix http:// to indicate that the page uses the HyperText Transfer Protocol). However, since this plain text means nothing to a computer, it uses DNS to convert the URL into the computer-readable address (known as an IP address) of the web server. The web is what is known as a client/server environment, where a server is a host computer that exists to serve clients’ requests (in this context, you’re the client).

The server duly retrieves the HTML code for the page you called for, and passes this back to your browser, which then interprets this code into what you see on your screen. If the page incorporates graphics or photos, the server merely passes all the necessary files along with the HTML code for your browser to assemble into the finished page; this is the simplest scenario. Now suppose the page incorporates code written in a server-side language, such as ASP, PHP or ColdFusion (which we use). The web server will recognise this by the page’s extension (.cfm in our case, short for ColdFusion Markup Language) and will therefore pass the request on to the ColdFusion server. This computer will then translate the CF code into HTML and pass this back to the web server. Incidentally this is why, if you view the source code for a CF page, you will only get to see the answer, never the question — which, if nothing else, protects the intellectual property of your CF code.

Taking this further, many server-side pages will incorporate a database query, invariably constructed using SQL (Structured Query Language). This is passed on to the database server, which retrieves the record(s) from the database and hands the result back to the CF server, which then incorporates this into the HTML code, and which is in turn passed back to the user. If all this sounds complicated, it isn’t really; it is merely a case of having separate computers each of which is dedicated to their part of the task in hand.