Compiled variables and backpatching

Hi, I'd be very interested to have an overview of compiled variable and backpatching within the interpreter. I can find plenty of emails and code that refers to the two topics, but none that defines them. If there is an overview somewhere, could somebody point me to it? If not, I have a few questions. Answers of any length are appreciated. What is a compiled variable? How does it differ from a non-compiled-variable? Why were they introduced? I presume that this is for performance - what performance impact do they have? What is backpatching? Is it related to compiled variables, or are they different concepts? Why was backpatching necessary? Is this performance related, and what performance impact does backpatching have? Thanks in advance, Paul -- Paul Biggar paul.biggar@gmail.com