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: