File servers are useful for sharing files across a network. With a file server, the client passes requests for file records over nerwork to file server.
The types of transparencies the NOS middleware is expected to provide are:-
Local/Remote access transparency
Distributed time transparency
Failure transparency and
It includes the communication stacks, distributed directories, authentication services, network time, RPC, Queuing services along with the network OS extensions such as the distributed file and print services.
With an object server, the Client/Server application is written as a set of communicating objects. Client object communicate with server objects using an Object Request Broker (ORB). The client invokes a method on a remote object. The ORB locates an instance of that object server class, invokes the requested method and returns the results to the client object. Server objects must provide support for concurrency and sharing. The ORB brings it all together.
An object is define ba a distrinct set up attribute that represent a network resources. For example User1 ,user2, group1 group2 etc.
Base services - It is a part of the standard OS.
Extended services - These are add-on modular software components that are layered on top of base service.