The documentation at http://learn.iis.net/page.aspx/1010/iis-75-express-readme/ says that:
Both 32-bit and 64-bit systems are supported, however only a 32-bit build of IIS 7.5 Express exists.
Why is this limitation there? are there any plans to get a 64-bit build?
I'm getting a lot of OOME using the 32-bit express on my test machine ... how were are supposed to simulate running on the real IIS, if the test server is so limited ...
IIS Express 8.0 has 64-bit support. At the time of writing it's an RC.
http://www.microsoft.com/en-us/download/details.aspx?id=34679
It's now here iisexpress_8_0_RTM_x64_en-US.msi -
http://www.microsoft.com/en-us/download/details.aspx?id=34679
This option is now part of Vs 2013 / 2015:
Tools -> Options -> Projects and Solutions -> Web Projects -> Use the 64 bit version of IIS Express
As of the date of this answer, there is no 64-bit build for IIS express. We all hope this changes sometime soon in the future.
来源：https://stackoverflow.com/questions/7345597/is-there-a-64-bit-build-of-iis-express-7-5