The biggest reason for upgrading from PHP4 to PHP5 is the end of life announcement made. As of December 2007 only critical security fixes will be made to PHP4. No support is being offered for PHP4 after August 2008.
Now is the time to migrate from PHP4 to PHP5. You do not want to wait until the last minute. As of right now you can migrate on your own terms, and take your time. The amount of difficulty in migrating from PHP4 to PHP5 will depend on your current code base. Some features enabled in PHP4 do not come enabled in PHP5 by default. Register Globals is one such feature.
PHP5 has the core functionality to support many of the new web technologies such as AJAX. Upgrading to PHP5 before August 2008 is a must. If you have a website that is still running PHP4, or you are not sure what version of PHP your website is running you need to find out. If you have access to your web server via FTP or a file manager do the following:
Open notepad (or equivalent text editor)
Enter the following code:
Save the file as phpinfo.php
Upload the file to your web server and execute it.
Displayed will be detailed information about your PHP build. You will see your current PHP version included with that information. If you are not using PHP5 and you wish to make the transition, please feel free to contact Storm Code and arrange for one of our project managers to take a look at your code base and give you an estimate on cost and time.