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!

  • how do I run the 32-bit version of IE8?  Apparently my HP laptop runs the 64-bit version because I get to all these websites that say I can't see anything without Adobe Flash 64-bit and there is no such thing yet, and so I should run the 32-bit version of IE8, but I don't know how to do that. I have the Microsoft automatic update, which I guess upgraded me to the 64-bit.  You say when you download the 64-bit, you automatically get the 32-bit too.  So I guess I have the 32-bit somewhere.  How do I access it and activate it instead of the 64-bit version?  Or should I just download a new 32-bit (and override the 64-bit, or do I have to remove the 64-bit first, and then reinstall the 32-bit?)

  • @Vicky: No, it is not correct to conclude that you must be running the 64-bit version just because Flash isn't working.

    "all these websites that say I can't see anything without Adobe Flash 64-bit"

    I have never seen any website with a message suggesting that you need "Adobe Flash 64-bit" which makes sense, because as you note, no such product currently exists. Can you point me to a site doing that please?

    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."  If it doesn't, you're using 32bit IE.

    As noted in the post above, you cannot "download the 32bit version"-- when you install the 64bit version, you automatically get the 32bit version as well. Users on 64bit computers have no way to download only one or the other.

    If you have a 64bit computer, your start menu will contain two links: "Internet Explorer" and "Internet Explorer (64-bit)".  

  • Eric,

    I've got a 32 bit IE 8 addon that doesn't seem to want to work.  From what I've read, both on your column and on the web, there should not be a problem with the addon functioning since, by default, it will be loaded into the 32 bit version of IE?  is that correct?

  • @MATT: Well, if you were explicitly starting 64bit IE and trying to use a page that used a 32bit addon, it would fail. But 32bit IE is the default, so this isn't typically a problem.

    What's the addon? What specifically happens?

  • How may I change Outlook Express to stop accessing IE8 (64-bit) when I click on a url in the body of the email and, instead, access the IE8 32 bit program that I use as a default browser?

  • @Jon: That *should* never happen unless your registry has been corrupted. Inside 32bit IE's Tools / Internet Options / Programs tab, is the "Make IE the default browser" button available/active?

    FWIW, the Outlook Express client has been replaced with an improved version called Windows Live Mail (see

  • The "Make IE the default browser" button available/active and is checked.  This is a clean direct install of XP x64 on a machine built from scratch.

  • To be more specific, the box about warning if the IE8 is not the default browser is available. the button about making it the default browser is viewable, but not available. I assume that it is that way because it's already been checked before.  There are no other active browsers on the computer.  I did migrate some xp 32 files from an older computer using the migration tool that xp provides.

  • So back to the original question.

    How may I change Outlook Express to stop accessing IE8 (64-bit) when I click on a url in the body of the email and, instead, access the IE8 32 bit program that I use as a default browser?

  • @Jon: Since I don't know how your computer could possibly get into such a state, I'm afraid I don't have any suggestion for you, other than to perhaps uninstall and reinstall IE8.

  • My OS is Win 7-64. I've read all of the posts, and I understand there should be 2 vers (32 & 64)of IE shown in my Start Menu, but I only see the 64bit ver.  I can't locate the 32bit version.  Where is it? How do I activate?

  • Clakat: If you type iexplore.exe in the run box, or start IE in pretty much any other way, you should find that you're running the 32 bit version.  The post above shows how to check.

    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."  

  • Hello Eric, I have a situation where I am truly preferring IE 8 x64 to be my default browser. I like the idea of no add-ons when surfing the net mainly due to concerns relating to vulnerabilities that exist within some of the add-ons. I could go on a rant about Adobe and Sun, but will refrain ;)

    Anyhow, I'm wondering when support for IE8x64 as default WILL be an option, and please say Vista will not be ignored! I'm not looking for any kind of registry hack, or moving files around and possibly breaking things, BUT IF I HAVE TO ...

    Please. This option. Soon? And in Vista too!

  • @Mike: No, changes of that nature are not typically taken outside of major browser releases.

  • Tom: Because most addons are not available for 64-bit, that means your problem is likely caused by buggy anti-virus or security software.

    You should try running in no add-ons mode explicitly ( just to be sure, but you should also ensure that you have the latest updates for AV/security software/Windows installed.

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