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Overview of the compatibility considerations for 32-bit programs on 64-bit versions of Windows Server 2003 and Windows XP
The WOW64 subsystem creates a 32-bit environment on the x64-based versions of Windows Server 2003 and of Windows XP Professional x64 Edition. Some 32-bit programs may run slower on these operating systems than they would on 32-bit versions of Windows Server 2003 and of Windows XP. For example, a 32-bit program might run slower on Windows XP Professional x64 Edition than it would on Microsoft Windows XP Professional. Alternatively, some 32-bit programs that require lots of memory may exhibit increased performance on the x64-based versions of Windows Server 2003 and of Windows XP Professional x64 Edition. This performance increase occurs because the x64-based versions of Windows Server 2003 and of Windows XP Professional x64 Edition support more physical memory than the 32-bit versions of Windows Server 2003 and of Windows XP Professional.
The WOW64 subsystem does not support the following programs:
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Programs that are compiled for 16-bit operating systems |
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Kernel-mode programs that are compiled for 32-bit operating systems |
A program that is compiled with the Microsoft .NET Framework will run as a 32-bit program in the WOW64 subsystem if the following conditions are true:
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The program has the ILONLY bit set in the header information. |
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The program was compiled with the Microsoft .NET Framework 1.1. |
If the program does not have the ILONLY bit set in the header information, or if the program was compiled with the Microsoft .NET Framework version 2.0, the program will run as a native 64-bit program.