Application I/O Interface

2. Network devices.
   • Because network access is inherently different from local disk access, most systems provide a separate interface for network devices.
   • One common and popular interface is the socket interface, which acts like a cable or pipeline connecting two entities over a network.
   • Data can be put into the socket at one end, and read out sequentially at the other end. Sockets are normally full-duplex, allowing for bi-directional data transfer.
   • Modern OSs have several network interfaces for various communication types. For instance, Windows provides one interface to the network interface card and a second interface to the network protocols.
3. Clock and Timer devices.
   • Several time-related services are needed in an OS: knowing the current time, checking how much time elapsed after a previous point in time, and counting the difference (in seconds or milliseconds) between two given timestamps.