Some aspects of the magnetic anisotropy of fine particles and thin films, employed in longitudinal recording media, are studied. The analysis is carried out through the measurement of perpendicular magnetization and the calculation of the second derivative, which allows to obtain the distribution of anisotropy fields. In assemblies of α-Fe metal particles, where shape anisotropy prevails, the evolution of the anisotropy field distribution with packing is studied. In Ba ferrite particles, where both magnetocrystalline and shape anisotropy are present and comparable, the effect of the ionic substitutions is analyzed. In thin film media, a comparison between magnetic layers with different composition (ternary and quaternary Co-based alloy) is carried out. In all materials, the relevance of the analysis of the whole distribution is underlined. From the anisotropy results, information on the magnetization switching is drawn.