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How Windows 64-bit Supports 32-bit Applications

Introduction

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.

 
Discussion

Windows 32-bit on Windows 64 (WOW64)

WOW64 emulates 32-bit Windows

Under 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

C:\WINDOWS\SysWOW64

For 64-bit applications, files are installed to:

C:\Program Files
C:\WINDOWS\SYSTEM32

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 isn't 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:

HKEY_LOCAL_MACHINE\Software

to:

HKEY_LOCAL_MACHINE\Software\WOW6432Node

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

HKEY_CURRENT_USER\Software\WOW6432Node

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.

Summary

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.

 
Related Links
 
Editor

This software category is maintained by volunteer editor Remah.

  "I've used TechSupportAlert and the older Support Alert Newsletter for almost a decade so I have saved hundreds of hours of work and many more dollars by following Gizmo's Freeware recommendations. Thanks for the opportunity to give something back."  

If you have had a similar experience then you should consider becoming a reviewer too.

Tags

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

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Comments

by Eagle2289 on 16. May 2014 - 14:14  (116247)

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.)

by sicknero on 17. May 2014 - 7:27  (116254)

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

by djperryboy on 9. April 2014 - 23:14  (115587)

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?

by sicknero on 14. April 2014 - 23:20  (115703)

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 - http://www.techsupportalert.com/content/cameyo-application-virtualizatio...

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.

by Remah on 14. April 2014 - 21:39  (115701)

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

by shriganesh on 12. March 2014 - 8:52  (114956)

A wow article on Wow64! Thanks!

by himadri sau on 24. October 2013 - 8:41  (111721)

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

by Remah on 24. October 2013 - 9:50  (111723)

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.

by skl_2k on 7. September 2013 - 4:22  (110569)

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.

by Remah on 3. October 2013 - 3:48  (111190)

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.

by exus69 on 10. April 2013 - 8:06  (106955)

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??

by Remah on 11. April 2013 - 6:45  (106985)

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.

by exus69 on 1. July 2013 - 7:07  (108869)

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

by Gravit (not verified) on 3. November 2012 - 8:14  (101785)

When I open Exe files, many times it gives an error message i.e., “The version of this file is not compatible with the version of Windows you’re running. Check your computer’s system information to see whether you need an x86 (32-bit) or x64 (64 bit) version of the program, and them contact the software publisher.” It's not a installation file but a single.exe file. Help me please. I am using Windows 7 Ultimate 64 bit. In 32 bit it never showed these errors.. Help ASAP.

by Remah on 3. November 2012 - 9:41  (101786)

This is a support question and any further help can be requested in our support forums.

You've probably identified the issue: it can't run in 64-bit Windows. This is mainly 16-bit installers (FYI, an installation program can still be a single .exe file) and 32-bit kernel drivers. Typically, this is older software.

Have you tried the simpler options?
1. Find for a newer version of the program.
2. Set the Compatibility options under the program's Properties (right mouse click or + ).
3. Find a version of the software that functions differently, either a portable (non-installable) version or one that doesn't use drivers.

The remaining options become much more difficult and time-consuming. You should back up all your files before starting. You may need to partition your disk drives to create various logical drives as well.
4. "Virtualization"
5. "Dual-booting with the old and new operating systems both installed".
6. Finally, if you can do without 64-bit Windows then install 32-bit Windows instead. This is clean install that will wipe everything on the system drive.

by shriber (not verified) on 31. August 2012 - 0:42  (98544)

And, none of them worked - none. I just saw the same canned responses from Microsoft over and over, and a lot of the same thing from other posters. I offered this fix, because I've been researching it for over a week now, and this problem stems back to 2007, maybe earlier, and it's STILL a problem, with Microsoft still AWOL on the issue. I just thought I'd offer what worked for me, but if you're not open to it ... And, of course I tried the logical fixes for the other programs if they seemed applicable, but I can't tell you how many times I saw:

Re-install Windows 7 - Seriously, I saw this so many times.
Do you have a virus?
Be sure you have the correct permissions.
Download & import a new msiserver.reg to your registry
Check that your Windows Installer is "started"
Uninstall your old versions first (this must be a 64-bit thing, because my 32-bit XP machine ran 2 versions just fine)

The only other logical fix other than the rename fix, was to actually replace the msiserver folder on the 64-bit machine with the folder from a working 32-bit machine. That made sense, and I would have tried that.

I am not a tech person, but I know my way around a computer enough to be open to this type of logical fix. It's a SETUP file - who's setting anything up anymore?

by Remah on 31. August 2012 - 1:09  (98545)

Reread my reply. I wasn't criticizing your response. I was pointing out that it works for more than just Excel and Word. It is the same registry modification as in the link you posted - I've just checked that to be sure.

Your problem is not a 64-bit Windows problem. It is a problem with the Office installation that also occurs on 32-bit Windows. It arises from running two versions of Microsoft Office together. It does not arise from running under 64-bit Windows.

As I said earlier, replacing the Windows installer folder won't help if the installer has already run.

I would have moved your posts to our support forum except that it is useful to show users what is not a WOW64 problem.

by shriber (not verified) on 31. August 2012 - 0:00  (98540)

I found a fix!! And, it was easy and logical!
- - - - - - - - - - - - - - - - - -
Rename 'setup.exe' to 'setup.old' in this folder:

C:\Program Files\Common Files\microsoft shared\OFFICE12\Office Setup Controller
- - - - - - - - - - - - - - - - - -

(I had to go to Program Files(x86) to find it)

http://uksbsguy.com/blogs/doverton/archive/2007/07/21/how-to-get-rid-of-the-installer-configuration-dialog-when-running-office-2007-and-office-2003-on-the-same-system-for-vista-and-other-versions-of-windows.aspx?CommentPosted=true#commentmessage

by Remah on 31. August 2012 - 0:20  (98542)

Microsoft has several pages addressing your issue. This is for all Office applications not just Word and Excel:
http://answers.microsoft.com/en-us/office/forum/office_2007-office_insta...

by shriber (not verified) on 30. August 2012 - 21:25  (98537)

I installed my Office Ultimate 2007 on a new Windows 7 64-bit machine, but Word & Excel won't load without configuring each time. Seems the concensus is to import the msiserver folder in the registry from the old 32-bit machine to replace the msifolder in the new 64-bit machine, since this one doesn't have a WOW64 in it for some reason. Why would some 64-bit systems have WOW64 after installing Office 2007, and some not? This makes absolutely no sense.

I had zero problems on my XP machine, and I had 2 versions of Office running, and used them together, all the time. MY analogy would be like going from a new car to a used one ...

by Remah on 31. August 2012 - 0:17  (98541)

It makes no sense because WOW64 is not missing in any of the support scenarios.

The configuration is not a Windows installer (msiserver) problem either. You would not get to the configuration dialog unless the installer had worked.

by John P (not verified) on 20. August 2012 - 14:33  (98019)

I am fascinated with this subjected matter of 32/64-bit operating systems and programs. I have gained some knowledge, and only a little some at that, and have come to the conclusion that I really should not be surprised at how it is all like a used car lot -- polish it, stick a new bumper on it, and wow! it still ain't very good. Thank you all.

by Remah on 23. August 2012 - 4:55  (98183)

It's better to be specific instead of using an analogy. The comparison with used cars makes no sense to me. In this article there is no equivalent to "a used car" that has been tidied up.

by Anonymouse (not verified) on 12. August 2012 - 17:03  (97610)

I think the comments made in response to this article simply reflect what 64-bit computing is to most people in reality: a confusing pain in the arse!

Regular users are unlikely to appreciate the performance gains in running 64bit program's and/or having access to 4+GB ram vs 3.5

The interchangeable use of processor architecture terminology does not help either: 32bit/x86/x86-32 & 64bit/x64/x86-64 etc

by Remah on 16. August 2012 - 20:53  (97829)

I agree. The transition to 64-bit computing spawned the changes in nomenclature which has only made it more confusing.

Even worse, the pain will extend as long as 32-bit operating systems continue to be published.

Incidentally, the benefits of improved memory management kick in well below the 3.5GB limit of Windows 32-bit.

by Caesar (not verified) on 28. May 2012 - 12:55  (94090)

Hi,
I have an existing windows Xp-32 bit server and i want to connect it with another server which is windows 7-64 bit. Will this things workout properly?
Please i need some advice on this matter..

Thanks!!

by Remah on 29. May 2012 - 4:22  (94124)

In general, there should be no problem connecting two different servers because they both support the same networking protocols.

Your question is not related to the topic of this tutorial. So any further other networking questions should be directed to a network support forum.

by Muskaan (not verified) on 21. May 2012 - 18:11  (93806)

i m using sony vaio 64 bit OS,,I am unable to run oracle related softwares on my computer...please help me out.

by pandey sumit (not verified) on 8. May 2012 - 6:21  (93199)

i am using windows7 64bit but when i install 32bit programs its show some error

by Remah on 29. May 2012 - 4:34  (94127)

Some 32-bit Windows programs or their installers will not run under 64-bit Windows.

For help with specific errors you should post in our support forum with exact details of the error message.