text: atm, vin, pin...  how many others can you think of? _  so, why do you think people say "atm machine" when they are really saying "automated teller machine machine"? _ because we are always in a hurry and are somewhat lazy!  there are millions of examples of acronyms, abbreviations, and initials we use daily like the ones you named.  text messaging took this to whole new level.    as far as the repetitive nature, of saying atm machine, pin number, i'm not sure why we do it.  maybe because we think people won't know what we mean?