Apache MPMs (Multi Processing Modules)

Apache uses the following MPM (Multi-Processing Module) for handling incoming requests and processes them.

Prefork
Prefork MPM launches multiple child processes. Each child process handle one connection at a time.

Worker
Worker MPM generates multiple child processes similar to prefork. Each child process runs many threads. Each thread handles one connection at a time.

Event
Event MPM allows more requests to be served simultaneously by passing off some processing work to supporting threads. Each process under Event also can contain multiple threads but, unlike Worker, each is capable of more than one task. Apache has the lowest resource requirements when used with the Event MPM.