Apache: The Definitive Guide, 3rd Edition

What Happens at the Server End?

We assume that the server is well set up and running Apache. What does Apache do? In the simplest terms, it gets a URL from the Internet, turns it into a filename, and sends the file (or its output if it is a program)^[9] back down the Internet. That’s all it does, and that’s all this book is about!

Two main cases arise:

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  The Unix server has a standalone Apache that listens to one or more ports (port 80 by default) on one or more IP addresses mapped onto the interfaces of its machine. In this mode (known as standalone mode ), Apache actually runs several copies of itself to handle multiple connections simultaneously.

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  On Windows, there is a single process with multiple threads. Each thread services a single connection. This currently limits Apache 1.3 to 64 simultaneous connections, because there’s a system limit of 64 objects for which you can wait at once. This is something of a disadvantage because a busy site can have several hundred simultaneous connections. It has been improved in Apache 2.0. The default maximim is now 1920 — but even that can be extended at compile time.

Both cases boil down to an Apache server with an incoming connection. Remember our first statement in this section, namely, that the object of the whole exercise is to resolve ...