.net Framework version folders?

Question

Looking at current folder structure :

c:\Windows\Microsoft.NET\Framework -
 1. v1.0.3705
 2. v1.1.4322
 3. v2.0.50727
 4. v3.0
 5. v3.5
 6. v4.0.30319

And on the 64 ver :

C:\Windows\Microsoft.NET\Framework64-
 1. v2.0.50727
 2. v3.0
 3. v3.5
 4. v4.0.30319

And here is my question :

I've installed today 4.5.1 :

But I don't see any folder for that version ( nor for 4.5).

If 3,3.5 are built on 2 and they do got special folder ( as you can see) - then why 4.5/4.5.1 didn't get their own folder ? what is so special about the way this version was embedded ?

Answer 1

Welcome to the big commotion of a year or two ago. 4.5 is a in place upgrade of 4.0, it overwrites files in the 4.0 folder to do the install.

UPDATE: I found this article that states you can still access the overwritten reference assemblies in C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework but those are not the assemblies that are used at runtime on your machine. If you have 4.5 installed a 4.0 targeted assembly will use the 4.5 dll's.