Some of the projects are running on PHP4 and while we require PHP5′s XML handling capabilities in our newer projects. Migration of the existing projects from PHP4 to PHP5, being quite a mammoth task, is out of the question. So I started looking out on the web for solutions to this problem.

I one solution from Tobias Schlitt’s Site on how to get both versions running on the same machine as Apache 1.3 modules. The only problem with this method is that the PHP files will have to be renamed to .php4 and .php5 to figure out which version of PHP apache has to call.

Another method I found was to compile two versions of Apache on the server and uses Apache’s mod_proxy to do some magic!
Here’s a link to the article: Running PHP 4 and PHP 5 Concurrently