GAC (Global Assembly Cache) is used where shared .NET assembly resides.Global Assembly Cache is used in the following situations:-
1) When the application has to be shared among several application.
2) When the assembly has some special security requirements like only administrators can remove the assembly. If the assembly is private then the simple delete of assembly the assembly file will remove the assembly.
How to add and remove an assembly from GAC?
There are two ways to install .NET assembly in GAC:-
(A) Using Microsoft Installer Package. You can get download of installer from https://www.microsoft.com.
(B) Using Gacutil. Goto "Visual Studio Command Prompt" and type "gacutil -i (assembly_name)", where (assembly_name) is the DLL name of the project.