Global Assembly Cache (GAC)

GAC (Global Assembly Cache) is a machine-wide cache of assemblies that allows .NET applications to share libraries. GAC stores assemblies specifically designated to be shared by several applications on the computer.

There are several ways to deploy an assembly into the global assembly cache:
Use an installer designed to work with the global assembly cache. This is the preferred option for installing assemblies into the global assembly cache.
Use a developer tool called the Global Assembly Cache tool (Gacutil.exe), provided by the .NET Framework SDK.
Use Windows Explorer to drag assemblies into the cache.
Note:In deployment scenarios, use Windows Installer 2.0 to install assemblies into the global assembly cache. Use Windows Explorer or the Global Assembly Cache tool only in development scenarios, because they do not provide assembly reference counting and other features provided when using the Windows Installer.