dired-jump

[Steven Merrill]

Can someone help me with the following problem?

I invoke gnu emacs 20.7.1 and open a dired buffer with C-x d. I pick a file 
from the dired list and begin editing. If I then try C-x C-j (dired-jump) 
nothing happens. C-h k indicates C-x C-j is undefined. If I then execute M-x 
dired-jump, I go back to the dired buffer as desired and then notice that C-x 
C-j is bound to dired-jump.

Why isn't C-x C-j bound to dired-jump initially when I invoke emacs?

Thanks in advance,
-steve