What determines the very first file that Vim will load on startup?

I am using Vim 7.4. I have a file /etc/vimrc, but when I vim a file and run the :scriptnames command, the very first file loaded is ~/.vimrc. 

On another Linux machine I also have Vim 7.4 installed, and when run the vim command and then run :scriptnames, that loads /etc/vimrc.

Where is this loading order determined? 

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