Installing Moodle/Creating custom php.ini files
From MoodleDocs
Critical to any installation using php is your php.ini file, which contains directives for you usage of php. This is especially true with respect to a number of moodle settings such as max upload and max post sizes with file upload
How php.ini is used
Sourcing
Search order and why that is important why phpinfo will not tell you what php.ini is being sourced site wide when you are suing php4
Invocation
Apached mod versus CGI Why you don't have to reread webserver files where you are using php via cgi
Manipulating php.ini
Editing the php.ini file generally
wrappers etc