Where does the magic 4 (C-u) come from?

Hi

I just had a discussion on #emacs on freenode about the origin of the
behavior of C-u and the multiplying by 4. None of us could find any
information about why 4 was chosen and if this behavior has been
borrowed from somewhere else.

So I figured someone here ought to know... What is the origin of the magic 4?

-- 
Deniz Dogan