Presentation Manager provides a number of specialized function and data type definitions (such as MRESULT, MPARAM, etc.) for use by Presentation Manager applications. While these type definitions are not "standard" C language types, their use is strongly recommended. OS/2 maps these type definitions into standard C language types using #define statements embedded in the OS/2 header file os2.h. Since the mapping may vary between OS/2 Version 1.3 and Version 2.0 due to differences between the 16-bit and 32-bit operating system architectures, the use of Presentation Manager's type definitions insulates the application source code from the underlying architecture.