The connection between the resistive-RAM (RRAM) operational-mechanism, performance, and utilized-dielectric-properties is described. Specifically, the atomic-level description of bi-polar hafnia-based RRAM, which operations involve the repeatable rupture/recreation of a localized conductive path, reveals that its performance is determined by the outcome of the initial forming process; defining the structural characteristics of the conductive filament and distribution of the oxygen ions released from the filament region. The ion distribution, in turn, is found to be linked to the level of dielectric oxygen deficiency, which may either assist or suppress the resistive switching process. With this improved understanding of the connection between RRAM performance and materials properties the optimization of RRAM devices may be more readily achieved.