How Windows 64-bit Supports 32-bit Applications



This article provides an overview of the Windows on Windows 64 (WOW64) sub-system and associated techniques that support 32-bit applications under Windows 64-bit.


Windows 32-bit on Windows 64 (WOW64)

WOW64 emulates 32-bit Windows

Win 32/64 bit imageUnder Windows 64-bit, 32-bit applications run on top of an emulation of a 32-bit operating system that is called Windows 32-bit on Windows 64-bit, or WOW64 for short.  WOW64 intercepts all operating system calls made by a 32-bit application.

For each operating system call made, WOW64 generates native 64-bit system calls, converting 32-bit data structures into 64-bit aligned structures. The appropriate native 64-bit system call is passed to the operating system kernel, and any output data from the 64-bit system call is converted into a format appropriate for the calling application before being passed back.

Like 32-bit applications, WOW64 runs in user mode so any errors that occur in translating an operating system call will only occur at that level. The 64-bit operating system kernel cannot be affected.

Since WOW64 runs in user mode, all 32-bit application code must also run in user mode. This explains why 32-bit kernel mode device drivers and applications that rely on them, will not work under Windows 64-bit.

The WOW64 emulator consists of the following DLLs, the only 64-bit DLLS that can be loaded into a 32-bit process:

Wow64.dll – the core emulation infrastructure and the links to the Ntoskrnl.exe entry-point functions.
Wow64Win.dll – the links to the Win32k.sys entry-point functions.
Wow64Cpu.dll – switches the processor from 32-bit to 64-bit mode.
Ntdll.dll – 64-bit version.

Wow64.dll loads the 32-bit version (x86) of Ntdll.dll and all necessary 32-bit DLLs which are mostly unmodified 32-bit binaries..However, some of these DLLs have been modified to behave differently on WOW64 than they do on 32-bit Windows. This is usually because they share memory with 64-bit system components.

WOW64 manages file and registry settings

In addition to handling operating system calls, the WOW64 interface needs to ensure that files and registry settings for 32-bit applications are kept apart from those for 64-bit applications. To achieve this two mechanisms are used, File and Registry Redirection and Key Reflection. Redirection maintains logical views of the data as if it were in 32-bit Windows and maps it to the correct physical location. Reflection ensures that 32-bit and 64-bit settings will be consistent where that is required.

File Redirection

File redirection ensures that there are separate folders for program and operating system files for 32- and 64-bit applications.

32-bit applications files are installed into

C:\Program Files(x86)

32-bit system files are installed into


For 64-bit applications, files are installed to:

C:\Program Files

The WOW64 file redirector ensures that requests from 32-bit applications to open files in C:\Program Files or C:\WINDOWS\SYSTEM32 are redirected to the appropriate 32-bit directories.

There is one issue with file redirection that users and developers should be aware of.

Many 64 bit applications still use 32 bit installation routines. To ensure that an application is installed correctly, i.e. to C:\Program Files, the installation routine should make an operating system call to temporarily suspend the WOW64 file redirector. After installation another operating system call needs to be made to re-enable the redirector. If this approach is not followed then the application will be installed to C:\Program Files (x86). A classic example of this is the 64 bit development version of Firefox 3.5, codenamed Shiretoko, which is installed to C:\Program Files(x86)\Shiretoko. Firefox still functions correctly, the only thing you can't do is change the icon for the application.

Registry Redirection

Registry keys specific to 32-bit applications are redirected from:




You may also occasionally see Registry entries elsewhere although this is unusual


This approach allows both the 32-bit and 64-bit versions of an application to be installed side-by-side without overwriting each other’s settings.

Registry reflection

Some redirected keys and/or values are also reflected. This means that if a 32-bit application makes a change to the redirected section of the registry, that change is also made to the 64 bit part of the registry, and vice-versa. Key reflection uses a policy of last writer wins. For example, if I install three applications with the same file extension then the last one to be installed will be associated with that extension.

  1. Install a 32-bit application that associates itself with the file extension XYZ.

  2. Install the 64-bit version of this application that associates itself with the file extension XYZ.

  3. Install another 32-bit application that associates itself with the file extension XYZ.

Double-clicking on a file with the extension XYZ in Explorer would load the application installed in step 3, as it was the last one to associate itself with this extension.

All of this is done transparently for 32-bit applications by WOW64, which, in intercepting calls to the operating system, detects references to file paths and registry keys and maps them accordingly.

WOW64 has several limitations

Some but not all 64-bit features are available to 32-bit applications

WOW64 provides 32-bit applications with access to some features of 64-bit systems. For example, applications can have more memory up to 4GB with the correct setting.. Other features are more limited due to overheads and restrictions. For example, 64-bit Windows will support logical 64 processors but 32-bit applications are restricted to the usual 32 logical processors.

Code Injection cannot mix between 32-bit and 64-bit

Under 64-bit Windows it is not possible to inject 32-bit code into a 64-bit process, nor is it possible to inject 64-bit code into a 32-bit process. Applications that rely on code injection to add functionality to existing applications will usually not work.

This explains why most 32-bit shell extensions do not work under Windows 64-bit. The majority of shell extensions rely on code injection to add themselves to Windows Explorer.

WOW64 does not support 16-bit installers

WOW64 provides support for Microsoft's 16-bit installer - by substituting a compatible 32-bit installer - but does not extend this support to third-party products.


Further options for running 32-bit applications with Windows 64-bit

Windows Virtual PC

Windows Virtual PC is free software that provides an environment that will support legacy hardware and software that will not work under Windows 7. Guest operating systems (OS) can run in a virtual machine which means they are not aware that they are running under another operating system.

The system requirements and features vary significantly between versions of Virtual PC and versions of Windows so check before you try Virtual PC. The latest version is, perhaps, the most limited with no support for operating systems before the current supported version of Windows XP which is Service Pack 3.

Windows XP Mode (XPM)

Windows XP Mode  is a specific implementation of Windows Virtual PC that comes with a pre-installed, licensed copy of Windows XP Professional with Service Pack 3. It is only available with the Enterprise, Ultimate and Professional editions of Windows 7 64-bit so you are expected to upgrade to these versions if you want it.

Many who have used XPM advise that it should be used as a last resort. It will provide legacy support if you have no other options but, compared to other virtualization products, performance is disappointing and the default configuration raises a number of security issues.

Dual boot Windows

You can install more than one version of Windows on the same computer by dual booting.For the purposes of this article, you would install a 32-bit version and a 64-bit version alongside each other. Each operating system is installed into its own disk partition and a boot manager is installed on the default partition to ensure that you can choose which operating system you want to use at startup.

Although you cannot use both operating systems at the same time it is a useful option because the entire computer is dedicated to the running operating system. Compared with virtual machines, there are no issues of compatibility and much less complexity in both installation and operation. You can also retain the ability to run 16-bit applications under the 32-bit version of Windows.


Most 32 bit applications will run quite happily under Windows 64. The main exceptions are:

  1. 32-bit device drivers.
  2. Applications that cannot function without the 32-bit device drivers that they use. Prime examples are antivirus, antimalware and firewall applications.
  3. Application extensions that rely on code injection into, for example, Explorer.

Some applications may work with reduced functionality. These include uninstallers, registry cleaners and tweaking programs, amongst others, since they only have access to that part of the Registry made visible to them by WOW64.

If you cannot run your 32-bit applications then consider virtualization or dual-booting with the old and new operating systems both installed.

Which runs faster 32-bit or 64-bit applications?

This question is asked a lot and there is no general rule because it depends on the application and which CPU features they use.

If we compared 32-bit and 64-bit applications in their native environments then 32-bit application usually use less memory than the equivalent 64-bit application because 64-bit versions use 64-bit values so they take up twice the space. The extra size affects the application startup and shutdown times and other activities that involve accessing the disk drives. Usually this means that the 32-bit application will run faster but 64-bit applications can access new and faster features in the 64-bit CPUs potentially giving improvements of up to 25% in processing speed.

Once both 32-bit and 64-bit versions of a program are running on 64-bit Windows you have to ignore any performance on a 32-bit CPU. The 32-bit application now requires WOW64 to run so that should be included in any performance comparison. This means you need to include all the duplicated resources used to map the 32-bit application to the 64-bit environment it runs under. Duplicated resources are used for memory mapping and redirection of files locations and registry entries. The result is that the 32-bit application uses more memory and runs slower than on an equivalent 32-bit CPU but it may still be faster than the 64-bit application.

Related Links

This software category is in need of an editor. If you would like to give something back to the freeware community by taking it over, check out this page for more details. You can then contact us from that page or by clicking here




Windows on Windows 64, WOW64, 32 Applications under 64 bit Windows, 64 bit Windows Vista, 64 bit Windows 7, Windows Virtual PC, virtualization, dual boot, Securable

Back to the top of the article.


Please rate this article: 

Your rating: None
Average: 4.2 (283 votes)


Article has fatal problem created by Microsoft for what my experience is on all Windows7 SP1 that I have checked. If you read into WOW64 you will find the use of setup16.exe in the code. For this file to operate it requires initialization file setup16.lst which is not found in the directory containing setup16.exe. This file setup16.exe is in many of the registry keys for working in the x86 environment. On my PC where I found WOW64 and scanned into the file there is setup16.exe. Therfore WOW64 is doomed to failure. In all my encounters with Microsoft support there is no recognition of any such file even though setup16.exe needs it. In decompiling setup16.exe the blank form for setup16.lst is found. If anyone has this *.lst file it is worth a fortune.

I'm not sure that there is a problem for Windows users. 64-bit Windows 7 (or 8/8.1 or 10) doesn't have 16-bit support so I doubt that there is any significance to not having setup16.lst or even setup16.exe.

How do i run Foxprow 2.6 that works fine on all 32bit windows on 64bit windows?
Not very happy with Dual boot OS and Virtual pc (vmware). Is there a simpler way out?
Pls assist. Thanks

Very Nicely explained..
But I have problem, I developed one software in witch is 32 bit application. But after installation of this software on windows 10, when i find my registry files in Local_Machine/software/wow6432Node is not present their. these files are present some other location. because of this my software dose not work properly. So give me some solution to come these file at wow6432node location.

Sorry, but such solutions are not provided on this site. Please look elsewhere.

Some additional WOW64 issues are covered at The WOW-Effect.

Thank you for an enlightening article. brings understanding that is much appreciated.

Okay so maybe this has been answered a dozen times already but I'd still like the help anyway. I have several 32-bit programs on my laptop (which is a 64-bit operating system)and I have WOW64 (i think) however whenever I try to run one of these 32-bit programs I get an error message saying that it cannot run. I need to know what I'm doing wrong, how do I get WOW64 to work? Or is there a different version I need? (for a bit more info a few of the programs are older games.)

WOW64 should do its thing automatically without your needing to do anything special yourself but, it doesn't work for all x86 software.

I have an install file that I believe originally was used for Windows NT 3.1 and so I wonder, Is there any possibility that it can be used in 64-bit Windows 7. This is a remake for a 32-bit windows XP i think but it seems to work for windows 7 32-bit also. I have tried to change the compability and also I used the automatic compability windows version including online help but it didn't solve my problem.

The message I get is when I open the program: "The version of this file is not compatible with the Windows version you have. Check the computers system information if you need a x86 or a x64-version (32-bit or 64-bit) of this program. Then contact the publisher of this program" (Translated). This is one of my favorite games since I was just a little kid. And I really, really, really want it to work. Any suggestions?

Also you could use Virtual Box to run an x86 version of Windows inside your x64 O/S, or you could as Remah says see if it's only the installer itself that is causing the problem. Trying unpacking the installer with 7-zip or Universal Extractor, you might get lucky and find that you can run it without installing it.

In the area of installation monitoring, you might also find this useful -

I've had mixed results with it but it will at the very least show you exactly what files/folders an installer creates and the locations of them, assuming you can find a pc that will let you run the installer.

Another alternative is to search the internet and see if there's another version of your game available; many old games have been re-created for newer O/Ss, there are also emulators like DosBox and some have been recreated to be played on-line in your browser.

It sounds like you have a 16-bit installer or application. If that is correct then you can use any of the "Further options for running 32-bit applications with Windows 64-bit".

If it is only the 16-bit installer that is the problem, ie the game is completely 32-bit, then you might be able to circumvent the 16-bit installation. You would use software that monitors the game installation on an older version of Windows and then replicates that configuration on Windows 7. I have never tried this so I'm unsure how well this could work as it does have some significant risks. If you decide to try this then some of the products in the following articles will help: Best Free Software Update Monitor Best Free Program Uninstaller

A wow article on Wow64! Thanks!

i am using windows7 64bit system but I want to install 32-bit applications under 64-bit system of Windows-7 plz help me,,,,,,

You will probably have no problems installing 32-bit application under 64-bit Windows. Read the summary again: "Most 32 bit applications will run quite happily under Windows 64". The summary also lists three reasons why a small minority of applications will not install.

I want to install 32-bit applications under 64-bit system of Windows-7 O/S, but the applications are not compatible. How can I able to install those applications under 64-bit O/S ? Please help me.

Which applications are you having problems with and what is the operating system? Most 32-bit Windows applications run without problems under 64-bit Windows.

Very nicely explained :) One quick question:

If I install 32 bit and 64 bit flavor of the same application on a 64 bit Win 7 will the 64 bit application work faster than its 32 bit counterpart or will it be the same according to the applications memory usage capacity??

The 64-bit versions should run faster and use less memory because all 32-bit code will be emulated by WOW64 in 64-bit Windows. Further explanation follows.

If we compared 32-bit and 64-bit applications in their native environments then 32-bit application usually use less memory and run faster than the equivalent 64-bit application. But once both versions are running on 64-bit Windows it is not sufficient to simply compare the two applications. The 32-bit application requires WOW64 to run so that should be included in any performance comparison. That means you need to include all the duplicated resources used to map the 32-bit application to the 64-bit environment it runs under. Duplicated resources are used for memory mapping and redirection of files locations and registry entries. The result is that the 32-bit application uses more memory and runs slower too.

Thanks for the reply. Really appreciate your deep knowledge on the topic :)