They all used to be N lenses, when the AF was driven by a motor inside the camera, not inside the lens. However, recently the AF motor has been integrated into the NII lens itself. As the aperture is controlled by the camera, the aperture ring has also disappeared from the lens. All future lenses will have a built-in AF motor, so it has been decided to standardize the names of all lenses with a built-in AF motor as "N", starting with the B008 released in December 2010.