Running 32-bit Applications

WOW64 is the x86 emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows. This allows for 32-bit (x86) Windows applications to run seamlessly in 64-bit (x64) Windows, as well as for 32-bit (x86) and 32-bit (ARM) Windows applications to run seamlessly in 64-bit (ARM64) Windows. WOW64 is provided with the operating system and does not have to be explicitly enabled. For more information, see WOW64 Implementation Details.

The system isolates 32-bit applications from 64-bit applications, which includes preventing file and registry collisions. Console, GUI, and service applications are supported. The system provides interoperability across the 32/64 boundary for scenarios such as cut and paste and COM. However, 32-bit processes cannot load 64-bit DLLs for execution, and 64-bit processes cannot load 32-bit DLLs for execution. This restriction does not apply to DLLs loaded as data files or image resource files; for more information, see LoadLibraryEx.

A 32-bit application can detect whether it is running under WOW64 by calling the IsWow64Process function (use IsWow64Process2 if targeting Windows 10). The application can obtain additional information about the processor by using the GetNativeSystemInfo function.

Note that 64-bit Windows does not support running 16-bit Windows-based applications. The primary reason is that handles have 32 significant bits on 64-bit Windows. Therefore, handles cannot be truncated and passed to 16-bit applications without loss of data. Attempts to launch 16-bit applications fail with the following error: ERROR_BAD_EXE_FORMAT.

In this Section

• Performance and Memory Consumption Under WOW64
• WOW64 Implementation Details
• Registry Redirector
• File System Redirector
• Memory Management
• Processor Affinity
• Interprocess Communication
• Application Installation
• Debugging WOW64