How does PHP actually work?

Is there some guide out there that describes how the PHP internals?

How files are loaded (required, included)?
How they are parsed and executed?
How memory is allocated?
How objects are created/destroyed?
How external modules are loaded?
How the stack/heap works?
How opcode caching actually work?
Common hacks and performance tips?

Solution

Sounds to me like you're you should look for resources on PHP Internal development. Looking for this information elsewhere will be really scattered.

I suggest picking up a PHP Core development book from your local book store and giving it a read. PHP.net has an underdeveloped beginners reference if you wanted to start there.