• 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.​​

The Global Assembly Cache (GAC) is a folder in Windows directory to store the .NET assemblies that are specifically designated to be shared by all applications executed on a system. 

Starting with the .NET Framework 4, the default location for the global assembly cache is %windir%\Microsoft.NET\assembly.

In earlier versions of the .NET Framework, the default location is %windir%\assembly.