The CS-RCS front-end and GNU RCS are two separate applications that run as separate Windows processes. The CS-RCS application is proprietary, but the GNU RCS application is distributed under the terms of the GNU GENERAL PUBLIC LICENSE (GPL). CS-RCS is not linked with RCS because such linking would violate the terms of the GPL. The Free Software Foundation affirms that running the two as separate processes, with a clean well-defined general interface between them, justifies the view that they are two separate programs.