1. A memory module comprising: first memory devices; second memory devices; a third memory device; and a memory buffer that transfers data with either the first memory devices or the second memory devices and transfers error checking information corresponding to the data with the third memory device, wherein the memory buffer determines an error address for transferring the error checking information with the third memory device based on whether the data transfer is with the first memory devices or the second memory devices, the error address indicating a location in the third memory device corresponding to the error checking information.