Disclosed is a phase change ink composition comprising a phase change ink carrier and a colorant compound of the formula . Each of a plurality of channel interface units and a cache memory unit as well as each of a plurality of disk interface units and the cache memory unit are connected through a switch and a data path network in each disk control cluster. The optical assembly further includes a hollow bonding sleeve having a sidewall having an inner periphery receivable over and affixed to the outer periphery of the optical collimator, an endwall having an aperture therethrough in facing relation to the optical-path end opening of the optical collimator; and an optical device in registry with the aperture of the endwall and affixed to the endwall. The stationary device and the mobile device are further configured to cooperatively measure properties of the power transmission system. Based on timestamp information in the latency responses, an estimated latency between the first and second MPLB components is determined. During a read operation of data from the memory cell, data is read out from the memory cell, and the data read out from the memory cell by destructive reading is written automatically to the guarantee cell, so that the data is retained securely as nonvolatile binary data regardless of operating condition, and thus loss of data can be suppressed.