A storage device includes a nonvolatile memory device and a controller. The controller provides the nonvolatile memory device with first data, an address, and a program start command and provides the nonvolatile memory device with second data after the program start command is provided the nonvolatile memory device. The nonvolatile memory device is configured to initiate a program operation, which is based on the first data, in response to the program start command and to continue to perform, based on the first data and the second data, the program operation when the second data is provided to the nonvolatile memory device. The nonvolatile memory device is configured to perform a program and a verification read of a first program loop based on the first data, the verification read of the first program loop being performed using one verification voltage.