This paper Presents information channel capacity as a fundamental measure of estimating the quality of digital communication channel which is possible with vanishingly small probability of bit error. This work presents that the capacity of a stationary channel with intersymbol interference (ISI) is achievable by both the techniques:1) single carrier modulation with ideal MMSE-DFE receiver and 2)multicarrier modulation over narrow subchannels with OFDM receivers. This result implies that both techniques single carrier or multicarrier, apart from different implementations, are essentially identical when it comes to criterion of achievable channel information capacity.