Recent operating systems provide the ability to perform versioning and scoping. This features make it possible to let PHP 3 and PHP 4 run as concurrent modules in one Apache server.
This feature is known to work on the following platforms:
To enable it, configure PHP 3 and PHP 4 to use APXS (--with-apxs) and the necessary link extensions (--enable-versioning). Otherwise, all standard installations instructions apply. For example:
$ ./configure \ --with-apxs=/apache/bin/apxs \ --enable-versioning \ --with-mysql \ --enable-track-vars