Open DMX is more of a communication protocol which is based on the FTDI 232BM USB to serial converter. With it, the PC does all of the formatting and timing issues that DMX requires and sends it in a format that the FTDI 232BM understands. It then converts it to a serial stream and sends it directly to a 485 chip for output to the DMX universe. While this makes the dongle inexpensive, it puts demands on the OC that Windows based PC's have issues with and unless you have a powerful clean running machine, you can wind up with dropped packets and glitching, especially if Windows decides to shift resources.