what is apache module and what kind of module it has?

Hi all,

I'm planning to make apache module.
I made php code. but it's too slow to handle requests for my project.
So i'm thinking if i replace php code to c and make apache module
then it maybe much faster.

upon above idea I have three questions.
1. Is it really worth to replace php code to c and make as apache
module?
2. It seems like that apache has two kind of module. One looks like
*.c and the
other is *.so.
If i regard that *.c is being compiled together with apache code
and *.so is exactly same as shared library then my idea is right or
there can be more difficult concept?
3. when the php is running as cgi does apache call php.exe and php.exe
interetes *.php file?

Thanks for reading,

Gijung Kim.