1. A memory accessing method for accessing a memory having a first memory rank connected to a first channel and a second memory rank connected to a second channel, the memory accessing method comprising: determining the memory capacity of the first memory rank and the memory capacity of the second memory rank; defining the first memory rank and the second memory rank as a virtual memory rank while the memory capacities of the first memory rank and the second memory rank are the same; accessing data of the virtual memory rank via both the first channel and the second channel simultaneously, wherein the memory is an asymmetrically arranged memory and at least have a third memory rank connected to the second channel; and accessing data of the third memory rank via the second channel.