By means of tight-binding quenched-molecular-dynamic simulations we have made a comparative study of the influence of both compressive and tensile strains on the growth mode in the case of the (Pt, Co) system. We show that the structural differences between the two situations can be explained in terms of asymmetry of the interatomic potential. In the compressive case (Pt/Co), a stress-driven alloy is formed at the coalescence of strained platinum islands. In the tensile case (Co/Pt), a discommensuration network develops allowing an over-closepacking of the film as for the (Ill)-Au reconstruction.