I bought a one of these a year or so back as I had to replace a motherboard (as it happens, in an old HP PC) and cheap motherboards don't have parallel ports. I'm using LinuxCNC at the moment so wanted to avoid the external motion controller route as there isn't much choice anyway. This PCI card has been working fine under Linux with a cheap BOB on the end of the parallel cable, but I can't speak for Mach3 use. I have built the PC as dual-boot and have Mach3 demo on the Windows half - I really should test it!