Question: 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).

Answer: 
There are a number of things Vim sets automatically if ~/.vimrc is present. Among them is `'nocompatible'` which affects a number of other options. Additionally, Vim does try to detect the proper values for other settings based on the environment. For example, the proper value `'background'` can often be auto-detected by Vim if invoked from an Xterm or compatible terminal emulator. The language settings will be based on your environmental variables.

Finally, you can run "`:scriptnames`" to see what files Vim has sourced since startup. This should include showing you where the system `vimrc` is located, if it exists.
To see where a particular option was last set, execute

```
:verbose set <option>?

```

To see the options that vim sets by itself, start vim as

```
vim -N -u NONE

```

then execute `:set`. In my case, running Vim 7.3.487 on Linux, I see

```
:set
--- Options ---
  helplang=en         scroll=11           ttymouse=xterm2
noloadplugins         ttyfast
  fileencodings=ucs-bom,utf-8,default,latin1
  background=light

```

To find out why any of those are set that way, use `:help`. For example, `:help 'ttyfast'` explains that it is set because vim determinded that my terminal is an xterm.