A nonvolatile memory system can include a nonvolatile memory device that can be configured to store data and a nonvolatile memory buffer circuit that can be configured to store data of a type that is predetermined to be flushed to the nonvolatile memory device in a sudden power off backup operation of the nonvolatile memory system, whereas a volatile memory buffer circuit can be configured to store other data of a type that is not to be flushed to the nonvolatile memory device in the sudden power off backup operation of the nonvolatile memory system. A memory controller can be coupled to the nonvolatile memory device, the nonvolatile memory buffer circuit, and to the volatile memory buffer circuit, where the memory controller can be configured to store received data or processed data in the nonvolatile memory buffer circuit responsive to determining that the received data or processed data is of the type that is predetermined to be flushed to the nonvolatile memory device in the sudden power off backup operation of the nonvolatile memory system.