A data storage system includes a read/write head having a tip connected to a resistive path locally exerting heat at the tip when an electrical current is applied; and a data storage medium from which information is reproduced by scanning a surface of the medium with a tip positioned in contact therewith, the medium comprising: a substrate; and a polymer recording surface within which data bit values are determined by the topographical state at the bit location, characterized in that the polymer contains thermally reversible crosslinkages.