Avoid Low-Level Operations in Windows Programs: Use DLLs

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

In the Microsoft Windows environment, an application should perform only those operations specified by the Windows application programming interface (API). Specifically, a Windows-based application should not:

1. Use processor I/O instructions.

2. Issue software interrupts.

3. Install interrupt handlers.

The Windows API has been designed to let programmers write applications in a hardware-independent fashion. However, some programmers may have noticed that the three operations mentioned previously can be performed from both Windows DLLs and applications.

Therefore, it may be tempting to avoid coding these operations in a DLL, especially if the DLL's only purpose is to execute functions that seem to operate correctly in an application. However, Microsoft strongly recommends against this practice, for the following two reasons:

1. Future Compatibility. Changes may be made to Windows in future versions such that applications that perform these operations directly may not execute reliably.

2. Portability. Applications that perform these operations directly will be more difficult to port to different hardware platforms (such as Windows running on a different machine architecture).