Apache is a powerful and flexible webserver, that has a very
modular architecture. Apache version 2 ports even the basic functionality of a web-server, such as binding to network ports on the machine, accepting requests, and dispatching children to handle the requests to a module named
Multi-Processing Module (MPM).
Using a modular approach even for this basic operation, makes Apache portable to a wider variety of Operating Systems. It also adds to the flexibility in using the Module that is apt for the scenario.