http://httpd.apache.org/docs/2.4/en/mod/mpm_common.html

The core engine in Apache is called the 'MPM' -“Multi Processing Modules”.

You can choose to change the MPM.

If you want to use PHP, you must use prefork.

• Each request/connection is handled by a process
• Multi-processes; 1 thread per process
• Eeach request is handled by a differentprocess.
• This MPM is chosen mainly for stability and security.

• Each request/connection is handled by a thread
• Multi-processes; multiple threads per process
• This MPM is chosen for better performance and lower memory consumption.

• It has been finally declared stable in Apache 2.4.
• The way it function is similar to the Worker MPM.
• it will assign a thread to a request.