404 not found!

The way it is working (and that part does work OK) is when I type localhost in the browser, the Users controller with the login function is running.

The question is "without modifying the default controller is there anyway for me to access function register() in Subit_backend.php from a xhr Extension"? I modified Subit_backend to be:

class Subit_backend extends CI_Controller
{

   public function __construct()
   {
       parent::__construct();

       $this->load->database();
       $this->load->helper('url');
         }


   public function register()
   {

   }
}

but when i type localhost/Subit_backend.php/register or localhost/Subit_backend/register or even just localhost/Subit_backend from the browser address bar I still get Error 404.

Can i assume that when I type localhost/Subit_backend/register I am actually typing c:/xampp/htdocs/Users/login/subit_backend/register ?

proof that an old dog can learn new tricks