Non-volatile data storage medium and system

A data storage medium (2) comprising a stacked plurality of layers (9), each layer composed of a layer material selected from a group comprising at least two different dielectric materials, adjacent layers being formed of different materials, and at least one of the layers, that is not a top layer, constituting an information layer (9i) configured to be modified locally by energy from an electromagnetic beam (7) having a specific beam wavelength and a propagation direction (Z) transverse to the layers. The stacked plurality of layers include an aperiodic layer arrangement including at least three stacked adjacent layers having different thicknesses with respect to each other.