What is with all of those different web pages? .htm, .html, .asp, .php, .cgi, .pl, .aspx?

Surf around the web for a while and you will notice that some of the web pages that you view have different file extensions. For example, this web page is titled web-page-extensions.htm. It could have been titled web-page-extensions.html though. So what is different between all of these extensions? Is a .asp better or worse than a .cgi extension? Or is everyone just being creative?

When your internet browser requests a web page from a web host it examines the file extension. If the extension is hyper text mark up language (.htm or .html) then it is rendered in your browser. If the extension is something else then, depending on what the extension is, the server software does something to the page and then sends you the page. What the server software does depends on what is written in the web page. And frequently the web pages are running programming scripts or mini-computer programs which are processing data before or after you arrive.

For example, if you have ever been to a web page which displays the IP address of where you are (an IP address is a numerical address of your computer on the internet), chances are the web page is a .php extension. Why? Because using the PHP language it is very easy to display this. What happens when you request the page with the .php extension is that the server software runs a computer script (a PHP language script in this case) and before the web page is displayed in your browser, it adds the results of the computer script. So the .php extension allows a web page to interact dynamically with each person visiting the site. Thus, each time someone visits the IP Address .php page they will see something different because the IP address of their computer is different from yours.

Some of the different extensions you will see are as follows:

.php (Hypertext Preprocessor Lanugage: Scripting language in the web page itself)

.asp (Active Server Pages: Another scripting language, found mainly on Microsoft Servers)

.aspx (.net technology: Microsoft's latest scripting ability and more, will be found on Microsoft Servers running the .net technology)

.cgi (Common Gateway Interface: Calls a computer program for caluculations or processing, computer program can be a wide variety of languages)

.pl (Perl Extension: Calls a Perl Script for processing)

So every time you see a web page with a different extension other than .htm or .html you know more is going on.

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