A storage device includes a nonvolatile memory and a memory controller. The nonvolatile memory performs read, write, and erase operations. The memory controller operates in an operating mode where the memory controller exchanges a voltage signal, set to a reference voltage level within an allowable range, with the nonvolatile memory or receives the voltage signal from an external device. When operating in the operating mode, the memory controller optimizes an operating frequency of the nonvolatile memory depending on a voltage level of the voltage signal and a temperature.