A method including estimating an access request frequency from a CPU to a memory subsystem by counting a number of CPU access requests and a number of requests other than CPU access requests, wherein the CPU is connected to the memory subsystem via a system bus, and the memory subsystem includes a memory controller connected to the system bus, and a DDR memory, including the estimated access request frequency with a predetermined threshold value stored in a register, generating a clock gate signal to decimate an operating clock of the memory controller in response to a result of comparing the estimated access request frequency with the predetermined threshold value, generating a dummy cycle signal to delay the timing of signal data output from the memory controller to the system bus, and generating a clock enable signal to decimate an operating clock of the DDR memory.