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:
Linux with recent binutils (binutils 22.214.171.124.25 tested)
Solaris 2.5 or better
FreeBSD (3.2, 4.0 tested)
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: