1. A PRML (partial response maximum likelihood) system, comprising: an analog-to-digital converter for receiving an analog input signal, and converting the analog input signal into a digital sampled signal according to a sampling clock; a branch estimator for receiving the digital sampled signal and estimating a plurality of branch eigenvalues; and a decoder for receiving the digital sampled signal and the plurality of branch eigenvalues and decoding the digital sampled signal to generate an output signal.