A large class of materials are known to transform from a crystalline to an amorphous structure under pressure changes at constant temperature. Among others, typical materials are water (H2O), quartz (SiO2) and berlinite (AlPO4). One of the striking (though rather controversial) properties observed in some pressure-induced amorphous materials is the so-called memory glass effect: when the amorphous sample is decompressed, the initial crystalline structure is recovered, conserving the original crystal orientation. Here, a model of interacting particles in two dimensions is studied in order to address some issues related to pressure induced amorphization and the memory glass effect. Two limit scenarios are presented according to the nature of the mechanical instabilities underlying the transformation: a direct crystal-to-amorphous transformation and a martensitic transformation. In the last case the product phase can be a poly-crystal with a very small grain size and the material can be easily taken as an amorphous material. The memory of this \"amorphous\" structure is a natural consequence of the underlying martensitic transformation.