For large or repetitive tasks in IIS (migrating sites, adding additional site bindings, etc.), modifying the applicaionHost.config can prove to be much simpler and efficient than using IIS Manager .  However one of the things I often hear from web administrators is “why are the changes I have made in the applicationHost.config not showing up in IIS”.  Though there could be multiple reasons for this, the most common reason is using a 32 bit editor to modify the applicationHost.confg on a 64 bit OS.  That’s right, if you use a 32 bit editor such as Notepad++ to edit your applicationHost.config in ‘C:\Windows\System32\inetsrv\config’ directory, you are actually opening/saving the applicationHost.confg in ‘C:\Windows\SysWOW64\inetsrv\Config’ regardless of what the title bar or save path may suggest in your editor.  This can lead to a lot of unnecessary confusion and troubleshooting if you don’t understand the fundamental concept of what is actually going on here.

Don’t believe?  Give it a try…

On a 64 bit server with IIS, browse to ‘C:\Windows\System32\inetsrv\config’ and open applicationHost.config using a 32 bit editor such as Notepad++.

Add some text to the comment section of the file and save.

Close Notepad++ and open the same file with a 64bit editor such as Windows Notepad.

Notice your change isn’t there.

Now browse to ‘C:\Windows\SysWOW64\inetsrv\Config’ and open applicationHost.config with Windows Notepad.  Notice your change was saved in this file.

In summary, when editing your applicationHost.config in a 64 bit OS, always be sure to use a 64 bit editor.