The National Institute of Standards and Technology has developed a modular definition of components for machine control, and a specification to their interfaces, with broad application to robots, machine tools, and coordinate measuring machines. These components include individual axis control, coordinate trajectory generation, discrete input/output, language interpretation, and task planning and execution. The intent of the specification is to support interoperability of components provided by independent vendors. NIST has installed a machine tool controller based on these interfaces on a 4-axis horizontal machining center at the Pontiac Powertrain Division of General Motors. The intent of this system is to validate that the interfaces are comprehensive enough to serve a demanding application, and to demonstrate several key concepts of open architecture controllers: component interoperability, controller scalability, and function extension. In particular, the GM-NIST Enhanced Machine Controller demonstrates interoperability of motion control hardware, scalability across computing platforms, and extensibility via user-defined graphical user interfaces. An important benefit of platform scalability is the ease with which the developers could test the controller in simulation before site installation. The EMC specifications are serving a larger goal of driving the development of true industry standards that will ultimately benefit users of machine tools, robots, and coordinate measuring machines. To this end, a consortium has been established and cooperative participation with the Department of Energy TEAM program and the US Air Force Title III program has been undertaken.