[ameswarb]

Apache is a process- and thread-driven application, but Nginx is event-driven. The practical effect of this design difference is that a small number of Nginx "worker" processes can plow through enormous stacks of requests without waiting on each other and without synchronizing; they just "close their eyes" and eat the proverbial elephant as fast as they can, one bite at a time.

Apache, by contrast, approaches large numbers of requests by spinning off more processes to handle them, typically consuming a lot of RAM as it does so. Apache looks at the elephant and thinks about how big it is as it tucks into its meal, and sometimes Apache gets a little anxious about the size of its repast. Nginx, on the other hand, just starts chomping.

The difference is summed up succinctly in a quote by Chris Lea on the Why Use Nginx? page: "Apache is like Microsoft Word, it has a million options but you only need six. Nginx does those six things, and it does five of them 50 times faster than Apache."

Source: http://arstechnica.com/business/2011/11/a-faster-web-server-...

[antihero]

Isn't Apache's default MPM event driven since 2.4 anyway?

[FooBarWidget]

event_mpm is only partially evented. Thanks to the Apache module API, which assumes blocking I/O, it's impossible for Apache to be fully evented. That said, event_mpm handles a lot of the important cases where evented I/O is desired.