Platform SDK: Win32 API

Behavior of Win32 Functions Inside 16-Bit Processes

When writing applications for Windows 95/98, you typically use 16-bit to 32-bit thunks for implementing callback thunks on 32-bit processes. You can also use them to execute 32-bit code in 16-bit processes. This method can improve performance and multitasking, but significant restrictions apply to 32-bit code executed in the context of a 16-bit process.

In general, 32-bit code running in the context of a 16-bit process should be limited to code that uses the 32-bit heap functions, memory-mapped file functions, file functions, and functions involving the current process and thread. You can also use GDI, dialog box, message box, and message functions from 32-bit code running in the context of a 16-bit process. You should avoid using third-party libraries unless you are sure they work safely in a 16-bit environment.