The IBM VisualAge C++ compiler, or another compatible compiler, and the Windows Software Development Kit are required to write user primitives. The user primitive DLLs must be created under Windows 95, Windows 98, or Windows NT.
User primitives must be placed in a separate DLL. The DLL name must be specified in the Smalltalk primitive declaration.
All 32-bit functions called using the PlatformFunction mechanism must be declared with the __stdcall calling convention.