Comparision between POSTGRES and PostgreSQL

Hello, people.

I'm triing to find some information, which relates POSTGRES and
PostgreSQL, for a class.

I was looking in the documentation, and in the book beeing written
("PostgreSQL: Introduction and Concepts", by Bruce Momjian) but I could
not find anything but instructions of the SQL sintax, some type
definitions. Well, the documentation is excelent (and I'm using it for
some projects of mine), but I need other kind of information.

Let me try to make myself clearer: I need something like "In the POSTGRES
design, the no-overwrite was used. In PostgreSQL we use..."

I saw in the documentation o the developer's corner, that the WAL is going
to be implemented in the 7.1 release. But what happened to the
no-overwrite approach?

Well, I hope you can help me. At least, pointing to some place/site where
I can find this kind of information,

TIA

Ricardo.