ok, read...
http://httpd.apache.org/docs/2.2/en/mod/
prefork - Implements a non-threaded, pre-forking web server
worker - Multi-Processing Module implementing a hybrid multi-threaded multi-process web server
http://httpd.apache.org/docs/2.2/misc/se...ml#dynamic
Embedded scripting options which run as part of the server itself, such as mod_php, mod_perl, mod_tcl, and mod_python, run under the identity of the server itself (see the User directive), and therefore scripts executed by these engines potentially can access anything the server user can. Some scripting engines may provide restrictions, but it is better to be safe and assume not.
And the other hand:
http://www.php.net/manual/en/install.unix.apache2.php
We do not recommend using a threaded MPM in production with Apache2. Use the prefork MPM instead, or use Apache1. For information on why, read the related FAQ entry on using Apache2 with a threaded MPM
hm...
there are plenty of websites to be read by you :-)