1. A non-volatile memory cell comprising: a volatile storage device that stores a corresponding logic state in response to electrical stimulus; and a shadow memory device coupled to the volatile storage device so as to receive and store the corresponding logic state, said shadow memory device including a non-volatile two-terminal nanotube switch, the two-terminal nanotube switch comprising first and second terminals and a nanotube article, the two-terminal nanotube switch storing the corresponding logic state of the shadow memory device in response to electrical stimulus applied only to at least one of the first and second terminals; wherein the non-volatile memory cell has a normal mode of operation and a low power retention mode of operation; wherein during the normal mode of operation the volatile storage device operates under nominal voltage; wherein during the lower power retention mode of operation the shadow memory device holds the corresponding logic state of the volatile storage device even when the volatile storage device operates under lower-than-nominal voltage.