# Why is the value of the ProgramFiles environment variable replaced with that of ProgramFiles\(x86\)?

Why is the value of the %ProgramFiles% environment variable replaced with the value of %ProgramFiles\(x86\)% when accessing it from a 32\-bit program launched in a 64\-bit operating system?

When a 32\-bit application launched in a 64\-bit Windows addresses the system environment variables %ProgramFiles% or %commonprogramfiles%, the [WoW64](https://pvs-studio.com/en/blog/terms/0056/) subsystem replaces the values of these variables with the values of the variables %ProgramFiles\(x86\)% and "%commonprogramfiles\(x86\)%\. Thus, for instance, %ProgramFiles% will be opened as "C:\\Program Files \(x86\)" when addressing from a 32\-bit program\.

This behavior is determined by the register redirection system that provides backward compatibility of 32\-bit software with 64\-bit operating systems\. The 32\-bit environment is emulated for 32\-bit programs even despite the fact that the data they are addressing is located in a different place\.

To avoid such a redirection in a 32\-bit program, you should use the %programfiles% or %COMMONPROGRAMFILES% \(i\.e\. with reverse case\) environment variables or the KEY\_WOW64\_64KEY flag when accessing the corresponding register nodes\.

To completely disable the file system redirection mechanism in the given thread, you may use the functions Wow64DisableWow64FsRedirection / Wow64RevertWow64FsRedirection but using them usually causes issues with implicit calls and delayed library loading\. Developers rarely have complete control over the whole input\-output process in the area between Wow64DisableWow64FsRedirection and Wow64RevertWow64FsRedirection and if code is implicitly loaded at the moment when the redirection mechanism is disabled, a 32\-bit application will most probably fail to get the necessary version of the library\. Alexey Pahunov, one of the WoW64 developers, [advises](https://blog.not-a-kernel-guy.com/2009/04/03/482/) to use this pair of functions only to wrap the call of the CreateFile function\.

## References

MSDN Library\. [Registry redirector](https://msdn.microsoft.com/en-us/library/aa384232(VS.85).aspx)