SESSIONS FILES

Hi all, I just started to work with SESSIONS in PHP. Its turning out to be a great way to keep user info alive across multiple pages. My question is, how long does a session temp file stored on the server exists for? Is it just for the current session? If the user shuts down their browser an turn is on again can I still call the original session? I just need to know that I am not creating multiple session files and cluttering up a server. New to this news group! is there a thread with rules? please post link... thx DRB