Yes, Mach3 (the software profram) will work with Windows 7, and windows 10 when coupled with the Mach3 USB interface. If you intend to use the parallel port driver, stick with Windows 7 in 32-bit mode.
Rnrmotion.dll is a dynamic link library which is very similar in function to an executable program, or app. Since a dll is executable, malicious code can be embedded in that type of file, so windows will automatically flag all files of this type. You just need to make sure you are downloading from a trusted source. The emotion.dll file on our site is clean, but still run run windows defender against it to make sure.
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Why does Windows 10 block the RnRmotion.dill for Mach3 USB interface from being downloaded?