Whats the difference between ND-3500(AG) and ND-3500?

I have been wondering whats the difference between ND-3500(AG) and ND-3500? What does the AG stand for?

They are both the same drive just the way people\sites choose to name them in device manager for example it is the NEC 3500AG but on some sites its named the NEC 3500 or NEC 3500A …