0~500mil. data group based on DQ0, isometric control within 25mil, between each data group to the clock line as a reference, isometric difference d4 data storage range 0~500mil. memory is used to store the program and a variety of data information of the memory components, memory can be divided into the main memory (referred to as the main memory or memory) and auxiliary memory (referred to as the auxiliary memory or external memory) of two categories.