A CRUM unit which is mountable/dismountable on an image forming apparatus is disclosed. The CRUM unit includes a power extracting circuit to, when a clock signal is received from an image forming apparatus, extract power from a high value of the clock signal and store in a capacitive element and a controller to operate using the extracted power, wherein the clock signal has a first pulse width in a data section where a data signal is received and transmitted, and has a second pulse width which is different from the first pulse width in an pause section where a data signal is not received.