.NET 4 newcomers may have realised that the old GAC location (%WINDIR%\Assembly) does not contain .NET 4 global assembly cache assemblies. Indeed, they have moved to %WINDIR%\Microsoft.NET\Assembly. It is worth noting that this folder does not use the shell extension that the older one uses, which prevents us from directly looking at the folder's contents, which, IMO, is nice (I mean, the new behavior). The old folder continues to host pre-.NET 4 assemblies.