Global Assembly Cache or GAC is machine wide. Basically it is way to keep DLL s globally without worrying about conflicts.
GAC or the Global Assembly Cache in .NET Framework acts as the central place for registering assemblies it means no more DLL HELL. 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 .Net Framework provides two tools for working with the cache. One is the windows shell extension that allows you to work with the cache using a Graphical User Interface (GUI) and the next one is command line tool called Global Assembly Cache (GAC) tool (Gacutil.exe).