Copy DLL from GAC

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This article demonstrates how to copy DLL from Global Assembly Cache.

The idea behind writing this article is to share solution to one problem that I faced recently for one my project. The problem was how we can copy an assembly (.DLL) file from Global Assembly Cache (GAC). Well, if it simply copy and paste then I am wasting my and your valuable time over here. There is no point have an article such as this. When you read the article heading, it looks pretty simple but it is not. Let’s first start with the basics.

The Basics

Assembly: According to MSDN Assemblies are the building blocks of .NET Framework applications; they form the fundamental unit of deployment, version control, reuse, activation scoping, and security permissions. An assembly is a collection of types and resources that are built to work together and form a logical unit of functionality. An assembly provides the common language runtime with the information it needs to be aware of type implementations.

There are two types of assembly 

  • Private: The assembly which is used only by a single application is called as private assembly.It does not require strong name and versioning.
  • Shared: Assembly which can be used across multiple applications is called shared assembly.
Click here to find more details about assembly. 

GAC (Global assembly cache):  GAC is a place where .NET assemblies are stored, specifically used to be shared by multiple applications on that computer. 

GACUtil is a command line tool which allows you to place, to remove assembly from GAC. 

To install an assembly called VirendraAssembly in the GAC, you can use the command

gacutil /i VirendraAssembly.dll

To uninstall an assembly called VirendraAssembly in the GAC, you can use the command

gacutil /u VirendraAssebmly.dll

I will not go into the details of gacutil you can find from this link

But have you ever tried to copy DLL from GAC (Global assembly cache)? Well, first time when someone asked me, I said go to GAC (c:\Windows\Assembly) folder, Select the assembly you want to copy, then right click on it and select copy option and paste it at your desired location. Well, I tried the same way but unfortunately there is no option available to copy when you make a right click on any assembly. Only available options are uninstall and properties option.

See the below screen shot.

One more thing that is noticeable is, go to DOS prompt and fire DIR command to see the listing of C:\Windows\Assembly folder and you will be surprised to see the listing. See below screen shot.

Where C:\Windows\Assembly folder looks like this.See Screenshot below:

Surprised!! Well, what you see on the DOS Prompt is the internal structure of GAC folder then why windows is not showing such structure of the GAC. Well, this is because off SHFusion.dll (Assembly cache Viewer). On the Dos Prompt fire Dir /AH command. It shows desktop.ini. SHFusion.dll uses this desktop.ini file to show abstract view of GAC. 

Various Techniques to show internal structure of GAC

There are 4 ways to show the same structure for GAC in windows as we will in DOS.

Rename the Desktop.ini file

As I mentioned previously, SHFusion.dll make use of desktop.ini to determine how to display the content of the GAC folder. From DOS prompt, fire these commands to rename the desktop.ini file.
attrib desktop.ini -h -r -s

rename desktop.ini desktop.ini.bak

Now, go to C:\Windows\Assembly folder to see its content. Screen will look something like below screenshot

You can also see the particular folder content. Select GAC and you will see something like this.

If you want to see both the view together run this series of commands on DOS Prompt.

Assuming you are on c:\ drive.

cd Windows\Assembly
attrib -r -h -s desktop.ini
mkdir OriginalView 
move desktop.ini OriginalView 
attrib +s OriginalView  
attrib +r +h +s OriginalView/desktop.ini

Now, go to assembly folder. You will internal structure of GAC and plus one more folder named OriginalView. When you go in this folder, you will see original view of GAC.

By Modifying the Registry

The following steps will modify the registry. If you make any incorrect entry in registry, that can cause some serious problems. Sometimes you may need to install operating system again. Use registry editor at your own risk. I prefer, before you follow these steps, take a backup of registry.
We need to add a key in registry that will disable the abstract view of the GAC.

To open registry editor, Go to Run and type regedit. Locate following registry, in the registry editor.

Right click on Fusion Folder and select New ->DWord Value.

Add a new Dword named “DisableCacheViewer” and set its value 1.

Now go to C:\Windows\Assembly folder and you will see folders in GAC.

By Uninstalling SHFusion.dll

Go to Visual Studio Command Prompt and fire this command to uninstall the SHFusion.dll
regsvr32 -u C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\shfusion.dll

Following message will appear.

Now go to C:\Windows\Assembly folder and you will see folders in GAC.

To get back to the previous state of view register the SHfusion.dll using the following command, fire this command on Visual Studio Command prompt.
regsvr32 C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\shfusion.dll

And you will see following message on the screen..

Now go to Assembly folder again and it will show the abstract view of GAC.

Using SUBST Command

Go to Windows DOS Prompt and type following command and press enter.
SUBST L: “C:\Windows\Assembly”

This command will create a virtual drive “L” and this drive will have the internal view of GAC, where C:\Windows\Assembly will have the abstract view of GAC
. Kindly ensure that the drive name that you type in SUBST command, it must not exist in your system. Go to My Computer and you will see the Drive named “L:”.

Now to delete this drive, run this command on command prompt.
This will delete the L: drive. 

By all above these four techniques, you can see the internal structure of GAC. Via Internal structure you can copy the DLL and paste it at desired location.

Now, let’s see what every folder contains in GAC. Mainly there are 5 Folders.
  1. GAC : This folder contains non-native images of DLL used in .NET Framework 1.x.

  2. GAC_32 : A 32-bit system will only have the GAC_32 directory.  A 64-bit system will have both the directory GAC_32 and GAC_64. These directories contain assemblies that are specific to 32-64 bit mode.

  3. GAC_MSIL: The GAC_MSIL cache contains assemblies that can be run in either 32-bit or 64-bit mode. They don’t have any dependency.

  4. NativeImage Framework Version :  Native image generated for Framework version. If you have .NET Framework 1.0 and 2.0 both, then there will be two directories.

  5. Temporary and Tmp : Temporary Directories.

The folder GAC, GAC_32, GAC_64 and GAC_MSIL contains non-native images of the DLLs. They all contain the MSIL that will be complied into native images and placed in NativeImage_Framework Version folder.



During this article, I have showed you various techniques to show internal structure of GAC and one can easily copy the DLL from the GAC folder and can paste it at desired location. I hope that readers will learn something new.

Kindly post your comments regarding feedback for this article.
Virendra Dugar

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About the Author

Full Name: Virendra Dugar
Member Level: Silver
Member Status: Member,MVP
Member Since: 8/11/2009 4:14:05 AM
Country: India
Virendra Dugar is experienced Senior Software Developer with over 5 years of hands-on experience working with Microsoft .NET technology (ASP.NET, C#, VB.NET,SQL Server). He is always keen to learn new technology. He holds a Master's Degree in Computer Application & Information technology from Gujarat University in india.In free time, he loves to listen music, read books, play games and do blogging etc. Visit his blogs :

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Comments or Responses

Posted by: Girinarra on: 11/16/2009
Good post
Posted by: Girinarra on: 11/16/2009
Good article

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