In a computer-implemented method of designing a nonvolatile memory device, first parameters associated with external environmental conditions are set. Second parameters associated with structural characteristics and internal environmental conditions are set. A first initial operation condition associated with an erase operation is determined based on the first and second parameters. A second initial operation condition associated with a program operation is determined based on the first and second parameters and the first initial operation condition. A final operation condition associated with reliability is determined based on the first and second parameters, and the first and second initial operation condition.