extensions & shared code

I may have missed this in the docs, but how does PHP allocate the code for extensions? does each instance of Apache have another copy of the PHP extension code? or do all Apache processes share the same code? and just out of curiousity, does each Apache process have another instance of the PHP code? (i'm asking about linux and a config where PHP is not a loadable module specifically, if it makes a difference) troy@recipezaar.com