1. A method for passing data of an external memory device through a buffer to a data processor comprising the steps of: dividing a storage region of the buffer into at least two variable subregions; passing first data read from the external memory device through one of said subregions to the data processor in response to a first data request from the data processor; passing the first data stored in one of said subregions directly to the data processor in response to a second data request when second data corresponding to the second data request is the same as said first data; passing second data read from the external memory device through another of said subregions to the data processor when said second data is different from said first data; and allocating a portion of the buffer for receiving identification data of the external memory device.