A method and an apparatus to detect data in a data storage device, and a method and an apparatus to effectively detect data in channels having characteristics in which bands of data to be reproduced are limited. The method includes partially selecting partial paths from paths of a Viterbi trellis having a number corresponding to an order of a polynomial used in equalization, in an order where path metric values increase from a path having a minimum path metric value, deciding a best path having a minimum path metric value among the partial paths, and detecting data based on the best path.