C-x 5 : split-window-horizontally

Dear Xemacs User,

I am an old emacs user... perhaps it is an xemacs thing, but it used to 
be that C-x 5 used to split the window horizontally... doesnt do it for 
me in xemacs. Is that by design ? I am planning to put the binding in my 
init.el file but don't want to mess up something in case it wasnt there 
for a good reason.

Thanks,
Tolga