The common hologram is an analog hologram containing photographic grey tones. A binary hologram contains only black or white areas and is made either by computer or by photographic hardclipping of analog holograms. Theoretically and experimentally, the signal/noise superiority of binary over analog holograms is demonstrated in this paper. The diffraction efficiency of binary holograms is typically ten times higher than that of analog holograms, while the noise due to the photographic grains is lower at the same time by a factor one half in the examples discussed. The discussion is presented in the context of holographic data storage with references to other applications where the signal/noise improvement is important.