Where are these non-default Vim settings stored if not in my .vimrc file?

So when I press :set I see a bunch of settings that are not on my ~/.vimrc file. (My guess is they're settings I've set years ago and don't remember).

So I do :version and get a path $VIM/vimrc, which is said to be "fall-back"ed by usr/share/vimrc. This is the "system vimrc".

I open the latter path, and the mystery settings are not in this vimrc file.

The only other path is the "user excrc file" at $HOME/.exrc, which I've no idea how to get to or what it is.

Anyone have any idea where the settings that show up when I command :set come from?

I'm on OS X (10.6).