The ITK Multi-Processing Module (MPM) works in about the same way as the classical "prefork" module (that is, without threads), except that it allows you to constrain each individual vhost to a particular system user. This allows you to run several different web sites on a single server without worrying that they will be able to read each others' files. This is a third-party MPM that is not included in the normal Apache httpd. . Please note that this MPM is somewhat less tested than the MPMs that come with Apache itself.