How does .net handle local .dll

When you copy a project through vs.net to a webserver it copies .dlls to the .net framework and the local bin directory right. Are these the same files. Which one is required? Shouldnt only the local one be required? Or are these two dll tied togethr somehow and if one fails to work the other also fails to work?

I understood it only copied the dll to your bin directory. Where else have you seen it copy it ?

In the .net framework folder so ive been told, but I dont have access to that folder on the server. So I cant confirm it.