Just to amplify what Jazz has said - I'm using my PCI card with LinuxCNC and it has not given me any problems. However, my current router is a very low-performance machine. My workshop PC where this is installed is dual-boot Linux and Win7. I have booted Windows with the trial version of Mach3 and it appears to detect the parallel port but I have not fully tested it. That's mainly because I plan to use an external motion controller with Mach3 for my next router to avoid any possibility of problems like compatibility, pulse timing, etc. The parallel port card will probably work. The external motion controller will definitely work. It's a personal decision!