Help.... files.el

[Praveen D V]

hi,
I have added
("\\.rb\\'" . ruby-mode)
to
auto-mode-alist.
I have done the same to "interpreter-mode-alist" and then
byte-compiled the file.  The corresponding .elc files also
show that "ruby-mode" is in those lists, but emacs doesn't seem
to recognize the file *.rb and set major-mode to
"ruby-mode".
When I look at these lists in emacs,
C-h v auto-mode-alist<RET>, they are not in the list.

Can somebody tell me if there some thing that I am missing?
TIA,
Praveen