1. 3.Data Communications 3.3Network Operating Systems

2. Operating Systems (OS)  The master control program that runs the computer.  It is the first program loaded when the computer is turned on, and its main part, called the "kernel," resides in memory at all times.  It may be developed by the vendor of the computer it's running in or by a third party.

3. Operating Systems (OS)  It is an important component of the computer system, because it sets the standards for the application programs that run in it.  All programs must "talk to" the operating system.

4. Functions of OS (explained by techweb.com)  User Interface  Job Management  Task Management  Data Management  Device Management  Security (From www.techweb.com)

5. Functions of OS  Program execution –Load the program into the main memory and run the program  I/O operations –Control the selection and use of input and output devices  File maintenance –Storage, create, delete and rename files  Error detection –Alert the user when errors occur, e.g. insufficient memory, power failure or out of paper (From Computer Studies for the New Generation, W.H.Kwan, Chung Tai Educational Press)

6. Functions of OS  Security control –Check the user identity and password. If an unauthorised user is suspected, the access right will be denied  Resources allocation –Allocate the CPU time, main memory and I/O devices to the user. Resources allocation is very important when the computer is shared by different users  Job scheduling –Set priorities for the jobs. The operating system has to arrange a job processing sequence for the CPU and to respond to computer users within an appropriate time (From Computer Studies for the New Generation, W.H.Kwan, Chung Tai Educational Press)

7. Network OS (NOS)  an operating system that manages network resources  manages multiple requests (inputs) concurrently and provides the security necessary in a multiuser environment  It may be a completely self-contained operating system, such as NetWare, UNIX and Windows NT, or it may require an existing operating system in order to function (LAN Server requires OS/2; LANtastic requires DOS, etc.) (From www.techweb.com)

8. More about NOS  In a peer-to-peer network, the network operating system allows each station to be both client and server  In a non-peer-to-peer network, dedicated servers are used, and files on a client machine cannot be retrieved by other users

9. More about NOS  In networks of PCs, NetWare is the most widely used network operating system. Windows NT, Windows for Workgroups, Windows 95/98, VINES, LAN Server, LAN Manager and LANtastic are also examples  UNIX, combined with TCP/IP and NFS, VMS combined with DECnet, the Mac OS combined with AppleTalk, and SNA, combined with VTAM and NCP, also provide network operating system services

10. Differences between OS and NOS  The main difference between an operating system and a network operating system is its multiuser capability  Operating systems, such as Macintosh System 7, DOS and Windows, are single user, designed for one person at a desktop computer  Windows NT and UNIX on the other hand are network operating systems, because they are designed to manage multiple user requests at the same time