Running a 32-bit program on a 64-bit operating system

run a 32-bit programThe WOW64 subsystem enables 32-bit programs to run without modification on the x64 version of Windows Server 2003 and the Windows XP Professional x64 version. The WOW64 subsystem is created by the x64 version of Windows Server 2003 and the Windows XP Professional x64 version of the 32-bit environment. For more information about the WOW64 subsystem, see the "Running 32-bit Application" topic in the 64-bit Windows section of the Microsoft platform SDK documentation. To view this document, visit the following Microsoft Web site: http://msdn2.microsoft.com/en-us/library/aa384249.aspx () http://msdn2.microsoft.com/ En-us/library/aa384249.aspx Program Performance ConsiderationsThe WOW64 subsystem creates a 32-bit environment based on the x64 version of Windows Server 2003 and the Windows XP Professional x64 Edition. Some 32-bit programs may run slower on these operating systems rather than on 32-bit editions of Windows Server 2003 and Windows XP. For example, a 32-bit program may run more slowly on Windows XP Professional x64 than it does on Microsoft Windows XP Professional Edition. Or, some 32-bit programs that require a lot of memory may exhibit higher performance based on the x64 version of Windows Server 2003 and the Windows XP Professional x64 Edition. This performance improvement is due to the x64 version of Windows Server 2003 and the Windows XP Professional x64 Edition that supports more physical memory than the 32-bit version of Windows Server 2003 and Windows XP Professional.

For more information about the differences between memory management between 64-bit and 32-bit versions of Windows, see the "Virtual address space" topic in this section for memory management in the Microsoft platform SDK documentation. To view this document, visit the following Microsoft Web site: http://msdn2.microsoft.com/en-us/library/aa366912.aspx () http://msdn2.microsoft.com/ En-us/library/aa366912.aspx limitations of the WOW64 subsystemThe WOW64 subsystem does not support the following programs: programs compiled for 16-bit operating systems are compiled into kernel-mode programs for 32-bit operating systems 16-bit program16-bit programs or 16-bit program components that are based on the x64 version of Windows Server 2003 and Windows XP Professional x64 are not supported. Software simulations that are required to run 16-bit programs on x64-based versions of Windows Server 2003 or Windows XP Professional version x64 can significantly reduce the performance of these programs.

A 16-bit installation is frequently used to install and configure 32-bit programs. In addition, some 32-bit programs require 16-bit components to function correctly. Although a 32-bit program that requires 16-bit components after installation may run correctly, you cannot use a 32-bit program that is installed by the 16-bit setup program. Programs that require 16-bit components cannot be run on x64 versions of Windows Server 2003 and Windows XP Professional version x64.

If a 32-bit program that tries to run a 16-bit file or component requires a 16-bit component, the 32-bit program logs an error message in the System log. The operating system will then let the 32-bit program handle the error.

To determine whether the program requires a 16-bit component, install and run the program. If the program generates an error message, the manufacturer of the program contacts a compatible update that is based on the x64 version of Windows Server 2003 and Windows XP Professional x64 Edition.

32-bit driver32-bit drivers are not supported on x64 versions of Windows Server 2003 and Windows XP Professional version x64. Drivers for all hardware device drivers and programs must be compiled specifically for Windows Server 2003 and Windows XP Professional version x64 based on the x64 release.

If you try to install a 32-bit driver on the computer, a 32-bit program that is running x64 version-based Windows Server 2003 SP1 or Windows XP Professional x64 version of the driver installation fails. In this scenario, or the Windows XP Professional x64 version of Windows Server 2003 SP1, the x64 version of the 32-bit program reports the error.

If you try to register a 32-bit program that automatically starts a 32-bit driver on a computer that is running a Windows Server 2003-based version of x64 or Windows XP Professional x64, recognize that the boot loader is not supported on the computer by a 32-bit driver. The 32-bit driver is not started for Windows Server 2003 or Windows XP Professional version x64, based on the x64 release, but does not start other registered drivers.

To determine whether the program requires a 32-bit driver, install and run the program. If the program generates an error message, the manufacturer of the program contacts a compatible update that is based on the x64 version of Windows Server 2003 and Windows XP Professional x64 Edition.

Other Precautions registry and file redirectionThe WOW64 subsystem isolates the 32-bit binary files from the 64-bit binaries by redirecting the registry calls and some file system calls. The WOW64 subsystem isolates the binary files to prevent the 32-bit binaries from accidentally accessing data from a 64-bit binary file. For example, a 32-bit binary file that runs a. dll file from the%SystemRoot%\System32 folder may inadvertently attempt to access a 64-bit. dll file that is incompatible with a 32-bit binary file. To prevent this, the WOW64 subsystem redirects access to the%systemroot%\syswow64 folder from the%SystemRoot%\System32 folder. This redirection prevents compatibility errors because it requires a. dll file that is specifically intended for use with 32-bit programs.

For more information about file system and registry redirection, see the "running 32-bit Applications" topic in the 64-bit Windows section of the Microsoft platform SDK documentation. To view this document, visit the following Microsoft Web site: http://msdn2.microsoft.com/en-us/library/aa384249.aspx () http://msdn2.microsoft.com/ The en-us/library/aa384249.aspx WOW64 subsystem redirects a 32-bit binary call without needing to change to a 32-bit binary file. However, you can see evidence of this redirection when you perform certain tasks. For example, if you type a command-line script at a 64-bit command prompt, you may not be able to access programs in the 32-bit Program Files folder at the command prompt. The WOW64 subsystem will be redirected and will be in the 32-bit program installer files (x86) folder. To access the correct folder, you must change the command-line script. In addition, you must type a command-line script at the 32-bit command prompt. The 32-bit command prompt automatically redirects file system calls to the correct 32-bit directory.

To start a 32-bit command prompt, follow these steps: Click Start, click Run, type%windir%\syswow64\cmd.exe, and then click OK.