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!

  • We, as IE users, keep being told WHY IE cannot be defaulted to 64Bit, but we are NOT told HOW we CAN do this once we know the pitfalls but want/need to change this.  What are you people at MS so worried about that  we cannot get a straight answer!?!

  • How come when my laptop upgraded to this internet 64--bit , I can't seem to play any video's, nor games. This is very confusing I wan't to know how I can get back to rag internet service, because I was in the middle of cafe world on facebook, and the internet 64-bit wan't allow me to finished the task, it says I need to unpgrade my adobe flash system, but when I tried, it said the internet-64-bit didn't run on it yet, so my quetion is why it do that in the frist place, is it a upgraded thing, if so I doesn;t really like the upgrade, i rather have the old internet service so howdo I get back on :) lol

  • @Ce'Kia: As explained in the post above, you are simply launching the wrong version of IE. It's not possible to remove 32bit IE even when 64bit IE is installed. So, simply find 32bit IE (usually in C:\Program Files (x86)\Internet Explorer\iexplore.exe) and launch that version instead of the 64bit version.

    @Corey: The reason you're not told "HOW" to do it is that it's both not supported, and there are technical reasons why defaulting to 64bit is *not possible*.

  • @EricLaw: I would like to hear these technical reasons for not being able to set 64-bit IE as default.

  • My question is that does Microsoft have any plan to introduce Just In Time  (JIT) script compiler in 64 bit IE 9 and when?

  • @Alvin: IE9 is now complete, and no, there will be no x64 JIT for this version. For IE9, the team focused our energy on the 32bit compiler, since 99.99%+ of browsing sessions are conducted using the 32bit browser.

    As I mentioned in the article above, the x64 version of IE9 still benefits from the improved interpreter and runs script benchmarks at ~500% faster than IE8, even without a JIT.

  • @EricLaw: Thanks, EricLaw for the informative reply. As for now, is it safe to assume that even 64-bit Internet Explorer 10 will not be developed to have its own JIT script compiler? I believe that most, if not all IE users are hoping that 64-bit IE will be slightly faster than 32-bit IE, thus encouraging all IE users to eventually migrate to 64-bit IE.

    Thanks for your information, EricLaw.

  • @Alvin: I'm not sure why you would jump to those conclusions, as neither (1> the JIT, or 2> the value of "migrating" to 64bit) is anything I've discussed in the context of future IE releases.

  • Eric,

    i was reading this blog post and am hoping you still get these comments.  I am having an issue....i have two 64-bit Windows 7 computers with IE8 (and I've tried IE9) that VBscript won't work when on the 32-bit IE but does work on the 64-bit IE.  I see on the web that others have also faced this situation...but i see no resolution.  Do you know of anything that might cause this?  I am desperate for a solution and anything you could offer would be appreciate.  I will check back on this blog...but i can also be reached at steve.fafel@missionresearch dot com.

    Thank you!


  • @Steve: It sounds like perhaps the VBScript.dll registration is corrupt in your 32bit instance. The DLL may need to be re-registered. What AV program do you have installed? Some AV engines try to inject themselves between IE and its script engines, and that might also be the culprit. Do VBS files work from the Cscript.exe or Wscript.exe programs?

  • Recently started having the problem listed earlier here where my 32-bit IE will not launch (well - it launches but then the window closes right away).  64-bit version works fine, but not all my programs will work when they need to access online.  when I try to launch the 32-but without add-ons, it still closes right away so I can't really de-bug or run that version without add-ons.  Any ideas how to restore the 32- bit version?

  • I am running IE9.  Pandora only works on the 64 bit option, not the 32 bit.  Why is that?

  • @Howie: My guess is that you've got a buggy Flash control installed in 32bit and Pandora is using the HTML5 Audio tag in 64bit because Flash is missing. But it's impossible to say without debugging it.

  • Thanks Eric.  I actually installed the flash that Pandora sugested and it still didn't work on the 32 bit IE9.  Besides working on the 64 bit IE9, Pandora also works on Chrome.  I just can't get it to work on the 32 bit IE9. By the way I have not had any problem with any other applications besides Pandora on the 32 bit IE9.  Really strange.

  • Now flash 11 supports 64bit Natively and Silverlight 5 will also support 64bit aint it time for Microsoft to release a 64bit version of the scripting engine and push 64bit browsing?

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