Global Assembly Cache is a machine-wide store used to hold assemblies that are 

intended to be shared by several applications on the machine. Each computer where the common language runtime (CLR) is installed has a global assembly cache. The global assembly cache stores the assemblies specifically

designated to be shared by several applications on the computer.

The .NET Framework provides two tools for working with the cache. One is a Windows shell extension that allows working with the cache using a Graphical User Interface (GUI). The other is a command line tool, called the Global Assembly Cache tool (Gacutil.exe).