This blog is closed as of 2/2015. @EricLaw left Microsoft in 2012, but was named an IE MVP in '13 & an IE userAgent ( in '14.

Q&A: 64-Bit Internet Explorer

Q&A: 64-Bit Internet Explorer

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From time to time, folks ask a variety of questions about 64bit IE.  I hope to answer the most common questions here.

NEW: Internet Explorer 10+ uses x64 in a fundamentally different way than IE7, IE8, and IE9, the versions for which the post below was written. By default, IE10+'s frame/manager process runs at 64bit, while Desktop Tab processes run in 32bit. Metro-style tab processes run at 64bit. A 64bit JIT was added to improve performance. You can learn more by reading a newer post.

Q: Can I install a 32bit version of IE on a 64bit version of Windows?

A: When you install the 64bit package, the 32bit version of IE will also be installed automatically.  You cannot install only the 32bit version on a 64bit operating system, because Internet Explorer updates OS platform components and must update both the 32bit and 64bit versions.

Q: As an end-user, how can I tell what bitness of IE I'm currently using?

A: To see if you're running the 64-bit version of IE, hit ALT+H to open the "Help" menu, and click "About Internet Explorer."  If you're running the 64bit version, this screen will say "64bit Edition." Alternatively, check out the x64 button add-on.

Q: From the server or from JavaScript, how can I tell what bitness of IE a web visitor is using?

A: The simplest method is to check the user-agent string.  See for more info.

Q: Why isn't 64bit IE the default browser?  Why can't I set the 64bit version of IE as the default browser?

A: This was an explicit choice made by the IE team, which may change at some point in the future.  The problem is that users might inadvertently get "stuck" using the 64bit version and not realize it.  This might cause some problems.

Q: Why?  What does not work properly with 64bit IE?

A: Browser addons, including BHOs, Toolbars, and ActiveX controls, must generally be the same bitness as IE itself.  So, if you are running a 64bit version of IE, any site that uses, say, Adobe Flash, isn't going to work until you install the 64bit version of the addon.  Sadly, almost no browser addons are currently available in 64bit versions, although that's somewhat likely to change in the future as 64bit Windows becomes more prevalent. 

There are two 64bit add-ons that I do recommend:

  • The 64bit version of Ralph Hare's most excellent mouse gestures addon
  • My x64 button, which allows you to easily recognize 64bit IE and reopen the current page in 32bit IE

 Q: What options/settings are shared between 32bit and 64bit IE?

Generally speaking, 32bit and 64bit share configuration settings wherever possible.


  • Homepage and favorites
  • Search providers
  • Web slices
  • Accelerators
  • Context Menu Extensions
  • Security Zone settings
  • Autocomplete information, including passwords
  • Cookies: persistent cookies are shared
  • HTML5 Storage: localStorage is shared

Not Shared

  • Binary add-ons: each only loads add-ons that are of the correct "bitness"
  • Cookies: session cookies are not shared
  • HTML5 Storage: sessionStorage is not shared

Q: Why does 64bit IE9 get faster JavaScript benchmark scores than IE8 (32 or 64) but slower scores than 32bit IE9?

In IE9 there's one other major difference between the 32bit and 64bit versions of IE. IE9 includes a new script interpreter which is much faster than the script interpreter in IE8. However, 32bit IE9 also includes a Just In Time (JIT) script compiler which converts script into machine code before running it. There is no JIT compiler for 64bit IE. So, for benchmarks like SunSpider (and script-heavy sites) 32bit IE9 runs script up to 4 times as fast as 64bit IE9 (which itself runs script around 5x as fast as IE8). So, you could end up paying a significant speed penalty when using 64bit IE9 vs using the default 32bit version.

Telemetry data shows that less than half of one percent of IE browsing sessions are conducted in the 64bit browser.

Note: IE10 Preview shipped a 64bit JavaScript JIT compiler, and the Windows 8 "Metro-style" browser (which will not load browser extensions) runs its tabs in 64bit processes.

Q: So, is there any benefit to using 64bit IE?

A: There are a few advantages to using the 64-bit version:

  • Security: DEP/NX is always on for 64bit processes. (Of course, on Vista SP1+, 32bit IE8+ has DEP/NX enabled by default too.)
  • Security: Memory protections like ASLR are more effective (because the address space is dramatically larger)
  • Security: Most bad guys only bother to write x86 shellcode, which will fail in an x64 process
  • It may crash less. (Because most addons don't load in 64bit IE, it tends to be more reliable.)
  • It may be faster to start up. (Because most addons aren't loaded. You can disable add-ons in 32bit IE if you'd like)

Q: Okay, so why offer 64bit IE at all? 

Because we have to.  :-) 

One thing to keep in mind is that Internet Explorer is basically the combination of a number of platform components, including the networking components (URLMon/WinINET), the rendering components (MSHTML), the script engines (JScript.dll/JScript9.dll, vbscript.dll) and a variety of other pieces that hold it all together. These components must be made available in 64bit versions so that 64bit applications can be built using these components.  Additionally, because Internet Explorer can be launched/created/used as a COM Server, we offer a 64bit version to enable hosting inside 64bit processes.

While we could have done work to make it harder for users to get to 64bit IE (e.g. by not creating a Start menu shortcut), I don't think there's any compelling reason to do so.

One day, 64bit IE might see a lot more use, as 64bit systems take over and 64bit add-ons become available.  Time will tell.

Got another question (or answer) about IEx64?  Let me know!

  • Does anybody know why my 32-bit IE isn't working on my laptop? My 64-bit is working just fine but my 32-bit isn't. I did have a Security Tool virus on my laptop a while back but I'm pretty sure I've completely removed it. So if anybody has any ideas, i'd appreciate them.

  • @Richard, the #1 cause for 32bit IE not working when 64bit IE does work is a buggy addon. You should follow the steps at

  • Commentary on 64-bit Silverlight:

    On an unrelated note, we recently had a case where a user had installed only a 64bit JVM and wondered why it wasn't working in IE. As you probably guessed, the problem was that he was running 32bit IE.

  • If you look back to the 9/21/09 question by Jon regarding making the 32-bit version the default when a link in an email is clicked, that is the question I came here to ask and was looking forward to the answer.  Alas, as having the 64-bit version be the default is supposed to be impossible, I must be stuck.  Or perhaps someone knows where in the registry I can look to fix the problem?

  • @Jan: Do you *only* see that problem from Outlook Express, or do you see it if you click START > RUN and type iexplore.exe?

  • When I typed in Alt+H and selected about internet explorer, it said it was 256 bit.  So is it 32 bit or 64 bit IE?

  • @Amy: "Cipher Strength: 256bit" means that you're on Windows Vista or later, which supports HTTPS ciphers as strong as 256bits.

    As noted in this post, the About screen will say "64bit Edition" for 64bit IE, and will not say that for 32bit IE.

  • @Bill, you should read,, and

  • Here is my quandry - CRM 4.0 opens links in IE x64, we have the CRM window show the user a SharePoint doc library on a tab. If the user clicks on a Word doc it opens, but without any toolbars what-so-ever. If I open the doc from IE x64 by browsing to the doc library directly(not using CRM) it will open. Everyone elses CRM opens links in 32 bit IE. I cannot get this users machine to open links in IE 32 bit. I am able to replicate this by setting an env var in PATH to the IE 64 bit. After removing teh PATH var it does not go back to IE 32 bit. WHat was once a working machine now suffers the same fate as my other user. Any ideas on how to get it back? I saw the post about 32 bit being default, but after removing IE 8 and Adding it back there is still no joy.

  • Had to reset user's profile in Windows 7 and uninstall-reinstall CRM. Just re-installing CRM does not fix it. It's got to be a setting in the user's profile where CRM or IE use the last program or path.

  • Jump Lists work for everything in 64bit Windows except for IE8 64bit.

    Why is this?

  • @John: It's a pretty arcane explanation:

    The jumplist on the 64-bit IE is always empty since the we cannot register both 32bit and 64bit IE's AppIDs for the file type handlers in the manifest without having separate protocol handlers for 32 bit and 64 bit.

  • Is it possible to have IE 32-bit open in one position (I have multiple monitors) with one home page, and IE 64-bit open in another position with another home page? Right now, clicking on the two different icons (32 & 64) produces the same home page and location.

  • @Gene: Alas, no, there's no code that attempts to support that scenario.

    You can obviously create multiple shortcuts that launch IE with different startup pages, but that's not specific to 32/64bit.

  • We have a similar problem with CRM 4.0.    It is opening in IE 64 bit by default and is that is a problem when trying to perform a mail merge.  HELP!

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