to OP: /proc/kcore is a file "representing" all your ram--so that's why it's so big. Similarly, you have other what you might want to think of as magic file or "pseudo-files", for instance /dev/hda "represents" your entire hard disk. So, if you opened the file in your favorite text editor (do NOT do this--it's just hypothetical), you'd be able to edit the data on your hard disk directly. Also, you have other useful magic files: /dev/zero consists of infinitely many instances of character number zero (which is not "0"; similarly character number 65 is "A" and not "65")--one might conceivable "copy" data from /dev/zero to /dev/hda to blank out the entire hard disk.
I hope this enlightens you more than it confuses you.