Different computer systems have different programming environments in spite of their similar capabilities. GEM and Macintosh software system both provide an operating environment in which the users can utilize all kinds of functions and routines to produce a user-friendly application program. Unfortunately, the programmers have to repeat the learning procedure and recode the source works if for some reason the application program is needed to run on both IBM PC and Macintosh microcomputers. In this thesis, a common interface is provided for programmers to reduce duplicated efforts and hopefully to get the same effects in both operating environments. Theses. (FR).