A plugin (sometimes referred to as a driver) allows people to add custom functionality to Mach3/Mach4. Plugins are written as .dll files in programming language in Mach3. Plugins for Mach4 include both a .sig and .m4pw file. They are primarily used to enable Mach3/Mach4 to work with hardware devices (e.g. external motion controllers), but can also be used to add functionality (e.g. Mach3’s Flash plugin) or extend existing functionality (e.g. Mach3’s Jcode plugin).
Visual C++ 2003 is required to create Mach3 plugins.