What is GAC?

A shared assembly has version constraints. It is stored in the Global Assembly Cache (GAC). GAC is a repository of shared assemblies maintained by the .NET runtime. The shared assemblies may be used by many applications. To make an assembly a shared assembly, it has to be strongly named.

To know more on how to share an assembly, create a strongly named assembly Click Here

GAC is located at C:\Windows\Assembly OR C:\Winnt\Assembly