Abstract: When the driver of a step motor is executed in a personal computer, its speed will be varied in response to the speed of the CPU. To provide a constant and stable speed of the step motor, the present invention automatically detects the system model and the CPU model of the personal computer when the host computer is power-on. In addition, the present invention establishes a lookup table which records a proper delay times for a corresponding system model and CPU model. After obtaining the CPU model and the system model, the proper delay times can be found by looking up the lookup table. The delay times obtained can be provided for the delay subroutine for the driver, thereby to update the delay parameter required for the delay subroutine. Consequently, the speed of the step motor will be automatically updated in response to the system performance of a personal computer to guarantee a smooth and stable stepping motion for a step motor.