I'm looking for information on the OS layer.I think it goes some thing like this . The user interface talks to application layer the application layer talks to the OS the OS talks to the Kernel the Kernel talk to the hardware. But I'm not sure where user level and system level is or why have a user level and system level at all. Also I was saying that Lion has a new Shell but one of the members was saying it is not The API is little different. The finder API is little different.