SysWOW64 and File System Redirector Explained

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Introduction

A Windows 64-bits OS has a SysWOW64 folder. It also has a System32 folder. These folders contain OS files and application DLLs. A 64-bit Windows has a system called WoW64, a Windows Operating (OS) system sub-system that runs 32-bit applications on a 64-bit OS.

SysWOW64 and System32 folders are both located in the %windir% folder, usually C:\Windows folder. On a 64-bit Windows, the %windir%\System32 directory is reserved for 64-bit applications. This allows 32-bits applications to run on a 64-bits Operating System.

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Tip
The reason you use %windir% instead of C:\Windows is that the Operating System may be installed in an partition other that C:\. %windir% is a Windows variable that defines the path to the OS installation.

This guide will explain the SysWOW64 folder and the WoW64 sub-system and what the SysWOW64 folder does in your computer. The guide will also cover which program folders 32 and 64-bits applications store their files in 32-bit OS and 64-bits Windows OS.

Important Notice
For a non-tech person reading this, I have done my best to explain this fairly tech topic in as much simplified language as I possible. My aim is that this guide works for both tech and non-tech readers.

Background of SysWOW64

Before 64-bits Windows OS was launched, a lot of 32-bits applications have been developed.

When 64-bits OS was launched, the 32-bits files of existing applications (they call them DLLs) are stored in a different folder %windir%\SysWOW64. On the other hand, 64-bits applications store their DLLs in %windir%\System32.

To hide the difference between the locations of 32-bits and 64-bits DLLs, Microsoft included WOW64 sub-system and SysWOW64 folder (%windir%\SysWOW64). The WOW64 sub-system hides this difference by using file system redirector (more on this shortly).

Use the Table of Contents below to navigate the topics discussed in this guide.

SysWOW64 and File System Redirector

On 64-bits Windows, when 32-bit application attempts to access 32-bits %windir% directories, they are redirected to the SysWOW64 path.

When a 32-bit application attempt to access %windir%\System32, %windir%\lastgood\system32, or %windir%\regedit.exe, the application is directed to the paths detailed in the table below:

Original Path Redirected Path for 32-bit (x86) Processes
%windir%\System32 %windir%\SysWOW64
%windir%\lastgood\system32 %windir%\lastgood\SysWOW64
%windir%\regedit.exe %windir%\SysWOW64\regedit.exe

SysWOW64, System32 and \Program Files Folders

In this section I will explain how applications work with a SysWOW64 and System32 folders 32-bits and 64-bits Windows.

On a 32-bits Windows Operating System (OS), application files are stored in %ProgramFiles% (usually C:\Program Files) folder. OS files are stored in %windir%\System32.

On a 64-bits OS, 64-bit applications store their files in %ProgramFiles% while OS files are stored in %windir%\System32 folder. On the other hand, 32-bits applications running on 64-bits OS store their files in %ProgramFiles(x86)% and core OS files on %windir%\SysWOW64.

To understand the seemingly confusing explanation above, in a 64-bits OS:

Program Files(x86) stores 32-bits application files
Program Files stores 64-bits application files

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SysWOW64 folder stores 32-bit files
System32 folder stores 64-bit files

syswow64
Tip
%ProgramFiles% is a Windows variable that points to the location of Program Files folder. %ProgramFiles(x86)% points to the Program Files(x86) folder.

Conclusion

The SysWOW64 is an important Windows folder that is only available in 64-bits Widows. SysWOW64 folder (full path %windir%\SysWOW64) store DLLs for 32-bits applications running in a 64-bits Window.

On a 64-bits system, WoW64 system sub-system creates a 32-bits layer that allows 32-bits applications to mimic a 32-bits Windows environment.

If you have any question or comment, use the “Leave a Reply” form at the end of this guide. Alternatively, you could share your experience with SysWOW64 folder.

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