Storage unit and circuit for shaping communication signal

A storage unit comprising:

• a channel control portion for receiving a data input/output request;
• a cache memory for storing data;
• a disk control portion for performing input/output processing on data in accordance with said data input/output request;
• a plurality of disk drives for storing data,
• wherein at least two of said disk drives input data to and output data from said disk control portion at different communication speeds relative to the communication speeds of the others of said disk drives,
• a generation portion for generating a clock signal by using a pulse signal transferred for communication between said disk control portion and said disk drives;
• an identification portion for identifying a frequency of said pulse signal;
• a frequency division portion for dividing a frequency of said clock signal at a frequency division ratio that corresponds to a frequency of said pulse signal;
• and
• a synchronization portion for synchronizing said pulse signal with a clock signal having said divided frequency,
• wherein said identification portion comprises:
• a charge accumulation portion for outputting a voltage that corresponds to a quantity of charge accumulated therein,
• a charge quantity variation portion for varying said quantity of said charge accumulated in said charge accumulation portion, at a certain variation rate,
• a charge quantity variation suppression portion for inhibiting said variation only during a certain lapse of time each time a signal level of said pulse signal is switched,
• a signal output portion for outputting a signal that corresponds to whether said voltage output from said charge accumulation portion satisfies a criterion,
• a time measurement portion for measuring a lapse of time that has elapsed since said quantity of said charge accumulated in said charge accumulation portion started to vary, and
• a frequency identification portion for identifying said frequency based on said lapse of time from a moment when said quantity of said charge started to vary to a moment when said signal that indicates that said voltage of said charge accumulation portion satisfies said criterion was output.