What is global assembly cache?

Each computer where the common language runtime is installed has a machine-wide code cache called the global assembly cache. The global assembly cache 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.