Due to the high device density and the advent of multiple bits per cell, modern nonvolatile memories are characterized by a non-deterministic behavior. We focus on phase-change memory (PCM), whose memory cell can be seen as a programmable resistor, and use information theory tools to investigate how the cell structure influences the storage capacity of this memory technology. In particular, we numerically compute the storage capacity of two known cell structures, i.e., the series cell, and the parallel cell. The results suggest that, in practical scenarios, the parallel cell structure is characterized by significantly larger storage capacity.