A memory system includes a memory controller; a first memory module, the first memory module including first volatile memory devices; a second memory module, the second memory module including nonvolatile memory devices; a data bus for transmitting data between the memory controller and the first memory module and between the memory controller and the second memory module; a first control bus for transmitting first control signals between the memory controller and the first memory module and between the memory controller and the second memory module; a second control bus for transmitting second control signals between the memory controller and the first memory module; and a third control bus for transmitting third control signals between the memory controller and the second memory module, wherein, in a backup operation, the second control bus and the third control bus are electrically coupled.