Can I run both PHP 4 and PHP 5 applications on my hosting account?
Yes, if your site runs Hosting Configuration 2.0, both PHP 4 and PHP 5 applications can run on your site. By default, PHP 5 files require the .php5 extension, whereas the .php extension will run under PHP 4. You can change these defaults through the htaccess file. See How do I use htaccess to manage file extensions? for more information.
If your site does not run the new hosting configuration and you want to upgrade, see How do I upgrade my hosting account to Hosting Configuration 2.0?.
NOTE: Changes made to an existing htaccess file will be seen immediately. When a new htaccess file is created or an existing htaccess file is deleted, however, these changes will not be seen until the htaccess cache is cleared. This occurs every hour.