Apache is not a monolithic server. New modules can be added to provide enhanced functionality, and existing modules can be removed to reduce the size of the server and improve performance. Apache 2 takes this modularization concept further and introduces three new ways of extending the server:
Multi Processing Modules (MPMs): Allow you to change the way Apache serves requests and improve the performance and scalability of the server.
Filtering Modules: Provide a way for modules to process the content provided by other modules.
Protocol Modules: The protocol layer has been abstracted, so it is possible for Apache to serve content using other protocols, such as ...