Questions about php.ini

I've signed up with a dedicated Web host that has PHP installed. The weird thing is that there is no php.ini anywhere. Is the file optional? Everything seems to be behaving okay. I have several Web sites that I'm setting up. Is it possible to use different php.ini files for each Web site? I'm using apache with mod-php. I see that PHP will search for php.ini in the working directory first. Does this mean that the way to accomplish what I want is to put a php.ini file in each directory that has .php files? It would be better if there was a way to have a php.ini file affect all files in a site, instead of putting php.ini files in all subdirectories of the site where there are .php files. Thanks! Jen