This chapter describes a set of elements specific to GPHIGS implementation. Implementation dependant parameters, extensions to the standard as well as the interface between GPHIGS and the X Window System or Windows GDI are described here. GPHIGS runs on many systems: UNIX, Open VMS, MS Windows 3.1, 95 or NT,... . The installation guide includes special features relative to each system. It should be noted that GPHIGS has a large number of drivers, each of which may have its own individual specifications, mainly related to capabilities and performance. It is therefore important to refer to the technical appendices supplied with the various drivers (e.g., Raster RLE, OpenGL, GL (for Silicon Graphics, IBM), xgl (SUN), PEXlib etc.), GDI (Windows).