The Microsoft Visual Studio 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.

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 ‘c’ or ‘cdecl’ calling convention.

All 64-bit functions called using the PlatformFunction mechanism must be declared with the ‘c’ calling convention.