Memory

[Bah__Name]

When a PHP session is active, where are the memory variables that are stored/created in the $SESSION superglobal residing, server memory or user/client memory?

[Mordecai]

They're kept in a file on the server. Consult your php.ini as to what directory it's in.
Search for "session.save_path."

[Wien]

on the HD of the server ! ! !
on my unix server the path is /tmp