Abstract: EFM (Eight to Fourteen Modulation) and its demodulation system nowused in optical disk drive is briefly described. The modulation encode chart and maincircuit logical graphs are given in this paper. The embodiments of both modulation anddemodulation are considered. Computer optimizing process is adopted, so the circuits ofdemodulation system are simplified. The addition of binding bits through simple logicalcircuits raises the rate of modulation.