apache2-mpm-prefork 2.2.14-5ubuntu8 (amd64 binary) in ubuntu lucid

 Each Apache Multi-Processing Module provides a different "flavor" of
 web server binary, compiled with a different processing model.
 .
 The prefork MPM provides a non-threaded, pre-forking implementation
 that handles requests in a manner similar to Apache 1.3. It is not as
 fast as threaded models, but is considered to be more stable. It is
 appropriate for sites that need to maintain compatibility with
 non-thread-safe libraries, and is the best MPM for isolating each
 request, so that a problem with a single request will not affect any
 other.