Wednesday, July 3, 2013

Network Operating System

Network Operating System 

A network operating system is a collection of software and associated protocols that allow a set of autonomous computers which are interconnected by a computer network to be used together in a convenient and cost-effective manner. In a network operating system, the users are aware of existence of multiple computers and can log in to remote machines and copy files from one machine to another machine.

Some of typical characteristics of network operating systems which make it different from distributed operating system are the followings:

Each computer has its own private operating system instead of running part of a global system wide operating system. 
Each user normally works on his/her own system; using a different system requires some kind of remote login, instead of having the operating system dynamically allocate processes to CPUs. 
Users are typically aware of where each of their files are kept and must move file from one system to another with explicit file transfer commands instead of having file placement managed by the operating system.
The system has little or no fault tolerance; if 5% of the personnel computers crash, only 5% of the users are out of business.

Network operating system offers many capabilities including:

-Allowing users to access the various resources of the network hosts

-Controlling access so that only users in the proper authorisation are allowed to access particular resources.

-Making the use of remote resources appear to be identical to the use of local resources

-Providing up-to-the minute network documentation on-line.

The key issue that distinguishes a network operating system from a distributed one is how aware the users are of the fact that multiple machines are being used. This visibility occurs in three primary areas; file system, protection and program execution.

File System: The important issue in file system is related to how a file is placed on one system from another in a network. 'Mere are two important approaches to this problem.

1. Running a special file transfer program

2. Specifying a path name

Running a special file transfer program: When connecting two or more systems together, the first issue that must be faced is how to access the rile system available on some other system. To deal with this issue user runs a special file transfer program that copies the needed remote file to the local machine, where they can then be accessed normally. Sometimes remote printing and mail is also handled this way. One of the best known examples of network that primarily support file transfer and mail via special programs is the UNIX's uucp  program and its network USENET.

Path name specification: The second approach in this direction is that programs from one machine can open files on another machine by providing a path name telling where the file is located. 

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