NET 4 0 has a new GAC why

Question

windir  Microsoft NET assembly  is the new GAC  Does it mean now we have to manage two GACs  one for  NET 2 0-3 5 applications and the other for  NET 4 0 applications   The question is  why

User · Accepted Answer

Yes since there are 2 distinct Global Assembly Cache (GAC), you will have to manage each of them individually.

In .NET Framework 4.0, the GAC went through a few changes. The GAC was split into two, one for each CLR.

The CLR version used for both .NET Framework 2.0 and .NET Framework 3.5 is CLR 2.0. There was no need in the previous two framework releases to split GAC. The problem of breaking older applications in Net Framework 4.0.

To avoid issues between CLR 2.0 and CLR 4.0 , the GAC is now split into private GAC’s for each runtime.The main change is that CLR v2.0 applications now cannot see CLR v4.0 assemblies in the GAC.

Source

Why?

It seems to be because there was a CLR change in .NET 4.0 but not in 2.0 to 3.5. The same thing happened with 1.1 to 2.0 CLR. It seems that the GAC has the ability to store different versions of assemblies as long as they are from the same CLR. They do not want to break old applications.

See the following information in MSDN about the GAC changes in 4.0.

For example, if both .NET 1.1 and .NET 2.0 shared the same GAC, then a .NET 1.1 application, loading an assembly from this shared GAC, could get .NET 2.0 assemblies, thereby breaking the .NET 1.1 application

The CLR version used for both .NET Framework 2.0 and .NET Framework 3.5 is CLR 2.0. As a result of this, there was no need in the previous two framework releases to split the GAC. The problem of breaking older (in this case, .NET 2.0) applications resurfaces in Net Framework 4.0 at which point CLR 4.0 released. Hence, to avoid interference issues between CLR 2.0 and CLR 4.0, the GAC is now split into private GACs for each runtime.

As the CLR is updated in future versions you can expect the same thing. If only the language changes then you can use the same GAC.

User · Answer

It doesn t make a lot of sense  the original GAC was already quite capable of storing different versions of assemblies   And there s little reason to assume a program will ever accidentally reference the wrong assembly  all the  NET 4 assemblies got the  AssemblyVersion  bumped up to 4 0 0 0   The new in-process side-by-side feature should not change this   My guess  there were already too many  NET projects out there that broke the  never reference anything in the GAC directly  rule   I ve seen it done on this site several times   Only one way to avoid breaking those projects  move the GAC   Back-compat is sacred at Microsoft

User · Answer

I also wanted to know why 2 GAC and found the following explanation by Mark Miller in the comments section of  NET 4 0 has 2 Global Assembly Cache  GAC       Mark Miller said       June 28  2010 12 13 PM      Thanks for   the post   Interference issues  was   intentionally vague  At the time of   writing  the issues were still being   investigated  but it was clear there   were several broken scenarios       For instance  some applications use   Assemby LoadWithPartialName to load   the highest version of an assembly  If   the highest version was compiled with   v4  then a v2  3 0 or 3 5  app could   not load it  and the app would crash    even if there were a version that   would have worked  Originally  we   partitioned the GAC under it s   original location  but that caused   some problems with windows upgrade   scenarios  Both of these involved code   that had already shipped  so we moved   our  version-partitioned GAC to   another place       This shouldn t have any impact to most   applications  and doesn t add any   maintenance burden  Both locations   should only be accessed or modified   using the native GAC APIs  which deal   with the partitioning as expected  The   places where this does surface are   through APIs that expose the paths of   the GAC such as GetCachePath  or   examining the path of mscorlib loaded   into managed code       It s worth noting that we modified GAC   locations when we released v2 as well   when we introduced architecture as   part of the assembly identity  Those   added GAC MSIL  GAC 32  and GAC 64    although all still under    windir  assembly  Unfortunately  that   wasn t an option for this release    Hope it helps future readers

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