A polarization mode dispersion generator for generating polarization mode dispersion spectra is provided. The front stage of the compressing sub-system is an octet based repeat compressor. The rotor is rotatable by an electromagnetic interaction with a stator, in which both sides of an end wall of each slot of the rotor core where the winding coil is inserted are respectively provided with a corner portion to connect both lateral walls of each slot. However, the arcuate-shaped lines on the other surface, the back surface, do not replicate the path of the recording head so the servo sampling rate is not constant but varies with radial position of the head. The abutment is dimensioned so as to engage the at least one recess of the projecting web of the hanger and is located proximal to the top wall relative to a midpoint of the cavity between the open end and the top wall. A queue manager may then store the sensed data file within a priority queue in association with the priority label, and independently of a temporal order of a time series of sensed data files.