HOWTO: IISExpress in 64 bit / 32 bit

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Background

he built in web server in Visual Studio (IIS Express for VS2010 and newer) is a convenient built in dev environment. It's much easier to use than full IIS and is the default for new web projects. While developing in a local copy of IIS may be needed for some customers, for those who want a simpler (zero configuration) development server, it's often quite suitable

The one big problem it's had has been that since Visual Studio itself is a 32 bit process, IISExpress was defaulted to running 32 bit. This has made it difficult to develop and test in 64 bit. For a long time, the solution was to use a local IIS instance.

However, it is possible to toggle IIS Express's "bitness" to 64 or 32

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VS2013 and newer

For Visual Studio 2013 and newer, this is a fully supported feature, built in and just needs a quick dive into the options menu

• Go to Tools -> Options on the main menu
• Then in the Options dialog, expand "Projects and Solutions"
• Now, go to the Web Projects tab
• Check (or uncheck) the "use the 64 bit version of IIS Express for Web Sites and Projects" checkbox
• Click OK

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VS2012

For Visual Studio 2012,it requires a registry hack

It is STRONGLY recommended to use VS2013 or later if you need IIS x64 support and not to use the registry hack as it's not 100% reliable

• Run Regedit
• Navigate to HKEY_CURRENT_USER\Software\Microsoft\VisualStudio\11.0\WebProjects
• if the RegDword Use64BitIISExpress exists, set its value to 1 to enable 64 bit (0 to use 32 bit)
• if the RegDword Use64BitIISExpress does not exist, create it and set to 1 to enable 64 bit (0 to use 32 bit)

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VS2010 and Older

The built in web server does not support x64 in VS2010 and older - if you must use one of these IDEs you'll need to use a local copy of IIS to develop/test in x64

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Related Links

•  INFO: Bitness Roundup Whitepaper: x86, x64, AnyCPU

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Original Article

• Q10450 - HOWTO: IISExpress in 64 bit / 32 bit
• HOWTO: IISExpress in 64 bit / 32 bit

Last Update

2025-06-18 - TD

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