I understand that I will have multiple machine.config files on a machine, 1 per framework version.  This brings me to a few questions.

1) Is there a single config file somewhere that I can put common entries in?  Specifically I am looking at a readonly connection string for a database that virtually every application we have needs.  We have console apps, windows services, and web applications in 1.1, 2.0, 3.5, and 4.0.

2) If I have a .NET 2.0 DLL called from a .NET 4.0 web application, which machine.config will the .NET 2.0 DLL be reading from?

3) How does 64-bit frameworks work into this?  If I have a 64-bit 4.0 app calling a 32-bit 2.0 DLL, which config file would the 32-bit 2.0 DLL read from?

Rhetorical: Why couldn't they just name them framework.config and then have 1 common machine.config?

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wls3Connect With a Mentor Commented:
Q 1:

I will assume IIS 7 for argument's sake.  The current structure of IIS 7 .config files is as follows:

machine | root web.config | site web.config | application web.config | directory web.config

Also, note that the IIS applicationHost.config file is parsed by the framework in considerations for the site web.config.  For your purposes, try adding entries to the root web.config (%systemroot%\system32\inetsrv\config) file.  To keep it clean, you can create a secondary file in the same directory and use the ApplicationManager class to access data within this file.  Check out the sample code in the link below for examples of how to access different configuration sets (application, machine, etc):

Note, this class was introduced with .NET 2.0, so, older apps (1.0/1.1) will be unable to utilize it.

Q 2:

The fully qualified assembly name is listed in one of the .config files.  It will automatically point to the appropriate run time, regardless of the version of the targeted application.  In short, a .NET 2.0 dll will read the 2.0 .config files.

Q 3:

You have to recompile 32-bit assemblies as 64-bit.  Here is a link for reference:

Since 32-bit assemblies use 4-byte pointers and 64-bit use 8-byte they are fundamentally incompatible.  If you were running a 32-bit app on a 64-bit machine, that is, however, doable.
SkipFireAuthor Commented:
After taking the time and setting up all the tests I found that the only thing that seems to matter is the version of the origination object, after that everything uses that config file.  So if you run a web application that is a 64-bit 4.0 DLL, my observations show that the .NET 64-bit 4.0 machine.config is read by all downstream DLLs.
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