Assemblies that should be used by all applications can be put in the global assembly cache. For example, if all applications should use an assembly located in the global assembly cache, a version policy statement can be added to the Machine.config file that redirects references to the assembly.

I dont think there is any GAC in ASP.NET but there is GAC in .NET which means global assembly cache which holds the information about the assemblies.I dont know what extent you know about assemblies but only strong assemblies can be added into GAC.search in google about assemblies .