1. An optical disc drive, comprising: a first storage unit, for storing compressed data; and a de-compressing means, for decompressing at least one part of the compressed data to generate de-compressed data, when the part of the compressed data meets a first predefined rule; a second storage unit, for storing the de-compressed data; a micro processor unit, for reading the de-compressed data from the second storage unit when the de-compressed data is needed for the following operations of the optical disc drive; and a compressor, for compressing at least one part of data randomly to generate the compressed data; wherein the micro processor unit determines or is informed which part of the data was compressed and where the compressed data is stored so that the compressed data can be read and de-compressed accordingly.