Just a quick note on how to browse physical location of Windows GAC. Normally if you browse to C:\Windows\Assembly using Windows Explorer it will give you this specialized view which looks similar to this:
You may saw the same behavior for Fonts folder also. So what’s wrong about this view? Well it doesn’t show you actual files and you can not see file size for example. Quick answer to this will be use of CLI (e.g. cd and dir commands or Get-ChildItem in PowerShell) or alternate file managers (e.g. Total Commander).
But in case you want to do this with Windows Explorer you may just type in the following path using Run menu or Windows Explorer address bar:
C:\windows\assembly\GAC_MSIL
Then move to the parent folder (by clicking on it in the explorer bar) to see all the GAC files in a normal explorer window. You can now copy, add and remove files as everywhere else.
See related question on stackoverflow.com – How to view the Folder and Files in GAC?