A microcomputer-based numerical control system for a lathe is studied with emphasis on designing the system software relating NC code date input via papertake reader and I/O panel signals to the hardware interpolator and the servo unit. For this, the system software with interfaces is constructed to fit Motorola's 16-bit μ-processor MC-68000 via a crossassembler for HP 3000 minicomputer so that the input data by paper tape reader be stored at temprary memory and then sorted and transferred to interpolator. Also I/O panel is designed to yield various information of the machine the operator wants while in operation.