WOW64 is the x86 emulator that allows 32-bit Windows-based applications to run seamlessly on 64-bit Windows.

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, and 64-bit processes cannot load 32-bit DLLs.

A 32-bit application can detect whether it is running under WOW64 by calling the IsWow64Process function. 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
• WOW64 Implementation Details
• Registry Redirector
• File System Redirector
• Memory Management
• Processor Affinity
• Interprocess Communication
• Application Installation
• Debugging WOW64

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Build date: 11/1/2007