Understanding the Global Assembly Cache (GAC) and Managing, Copying DLLs from Global Assembly Cache

Most of you may confuse why there are two GACs available in the machine.

• C:\WINDOWS\assembly
• C:\WINDOWS\Microsoft.NET\assembly

What is GAC

GAC is a shared location in your machine that keeps assemblies, DLLs for common sharing purpose. Assume that you are using system.data.dll in your project. So one option is you can place the DLL with your project. But assume you are creating another project which is also using the same .NET assembly system.data.dll, so it is better to have it in a common place where that can be referred.

Since it is a common framework DLL and used separately from your application logic, it is good to place in a shared place for ease of maintenance and update process.

What is C:\WINDOWS\assembly

Previous CLRs use this place as its common location for DLLs. Previous CRLs include versions 1.0,1.1,2.0. these CRLs versions are used before .NET framework 4.

• .NET Framework 1.0 - CLR v1.0
• .NET Framework 1.1 - CLR v1.1
• .NET Framework 2.0 - CLR v2.0
• .NET Framework 3.0 - CLR v2.0
• .NET Framework 3.5 - CLR v2.0

So if you are working with an application that belongs to these versions; this is the place for your global assembly cache.

What is C:\WINDOWS\Microsoft.NET\assembly

After CLR version 4.0, Microsoft changes their location to this for maintaining and avoid loading wrong DLLs in applications for backward compatibility.

• .NET Framework 4.0 - CLR v4.0
• .NET Framework 4.5 - CLR v4.0
• .NET Framework 4.5.1 CLR v4.0
• .NET Framework 4.5.2 CLR v4.0

So if you are engaging with application after .NET Framework 4.0; this is the default location for its assemblies.

Managing and Copying DLLs from Global Assembly Cache

• shfusion.dll
• Gacutil.exe

shfusion.dll

This is a windows shell extension which shifts before Framework 4.0 to manage DLLs in GAC.

If you navigate to C:\WINDOWS\assembly from your file explorer, you can see something like this that you cannot manipulate.

So you can use the following command to manipulate it.

• Goto command prompt (cmd) and open it as run as Administrator
• Then run the command

C:\Windows\system32>regsvr32 /u  C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\shfusion.dll

When you click enter, it will prompt with a message like below which turns your GAC into manageable state.

If you navigate to C:\WINDOWS\assembly ; you can see it yourself.

You can revert it back to normal by registering the DLL again.

C:\Windows\system32>regsvr32 C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\shfusion.dll

shfusion.dll is only available till Framework 4.0 and its versions. Now it is discontinued and is not shipping with the framework. If you are having multiple versions installed, use the latest framework folder.

EX: Microsoft.NET\Framework\<.NET version> \shfusion.dll

Gacutil.exe

This is the alternative if you are dealing with DLLs after 4.0 you need to use the gacutil.exe. You can type gacutil in Visual Studio command prompt and get a list of commands available for DLL manipulating.