Discrete memory is a phenomenon observed in elastic‐plastic materials with a material memory of a restricted type. Instead of the entire stress path, only a discrete set of stress reversal points is memorized. For certain types of stress path, parts of the discrete memory can be completely erased. In a series of experiments in which brittle rock was stressed under triaxial conditions, I have found that rock exhibits discrete memory which is associated with the phenomenon of dilatancy. Dilatancy in rock is characterized by an inelastic increase in volume strain that occurs when the sample is subjected to differential compressive stresses. The microcracking responsible for the inelastic strain produces substantial changes in elastic wave velocities. To very high precision the strains and elastic waves velocities in dilatant rock show discrete memory. Memory of maxima and minima of the stress difference can be developed, with multiple points remembered simultaneously. Discrete memory provides a strong constraint on possible mechanisms of dilatancy and brittle failure. Two models have been proposed for the basic crack mechanism: a shear crack and a tensile crack. Analysis of the shear crack shows that qualitatively it is capable of generating the observed properties but there are important details of discrete memory that are difficult to explain using this model. An analysis of the response of a tensile crack to cyclic loading, together with the introduction of an energy‐dissipating function, shows that a stable population of such cracks can produce discrete memory. The origin of the energy dissipation is not clear.