Network Operating Systems
The purpose of a computer network is to allow users to share resources located on other computers, to share hardware devices such as printers and fax machines, to allow applications running on different computers to exchange data and to allow users to communicate electronically. A network operating system (NOS) is a special kind of operating system designed to provide networking functionality. A network operating system should support client-server networking, and include all of the programs needed to manage network resources and create a secure network environment. The most widely used network operating systems today include Microsoft Windows Server, Novell Netware, UNIX and Linux. Most network operating systems provide the following functionality:
- Creation and management of user accounts
- Configuration and management of network resources
- Authentication of network client computers and users
- Communication services
- Network monitoring and troubleshooting
The network operating system is deployed on network servers to enable administrators to manage network resources such as data storage areas, network printers and communication services. Because most organisations are increasingly dependant on computing services, and also partly due to the phenomenal growth of the Internet and the World Wide Web, the number of users on a typical enterprise LAN is growing almost daily. Keeping track of all these users and the resources they need is becoming increasingly difficult, time consuming and costly. One of the most important facilities provided by any network operating system is a set of utilities that allow the administrator to create and manage user accounts effectively. One of the network administrator’s first tasks when setting up a network will be to create a directory services structure. This involves populating a large, hierarchical database known as the directory services database with information about network users and resources. The database holds a list of the resources available to each user, and the privileges granted to each user for each resource. The administrator will also need to set up an appropriate network file system. The network operating system provides the tools required to carry out these and many other tasks, including the implementation of network security policies, optimising system performance, backing up and restoring data, installing and configuring distributed applications, and monitoring and managing network usage and performance.
Multi-user operating systems such as UNIX which were originally written for mainframe computer systems have been around for a very long time (since the 1960s, in fact), and were designed from the start to support networking. Single-user desktop systems such as MS-DOS came into existence with the personal computer, and whilst having limited networking functionality, were not really designed with networks in mind. More recently, GUI-based desktop operating systems such as Windows 95 and its successors have added increasingly sophisticated support for networking. In the Microsoft world, however, there is a clear distinction between network operating systems (deployed on network file servers) and desktop operating systems that support networking (typically deployed on home computers or on corporate network client computers). Linux distributions have retained many of the characteristics of UNIX (unsurprisingly, since Linux essentially started life as an open source version of UNIX), and can be configured either for desktop use or as a network server.
Appropriate client software must also be installed on network client computers to allow users to log on to a server and access network resources. Most desktop operating systems provide built in client software that allows legitimate users of the network to authenticate themselves to a network server by providing a valid username and password. Windows desktop operating systems such as XP, Vista and Windows 7 all provide client software that allows the user to connect to a Windows-based network. In some organisations, network operating systems like Novell's Open Enterprise Server are deployed on network file servers, while the client workstations usually have a Windows desktop operating system installed. In this situation, Novell client software will be installed on the client computers to enable them to authenticate to a Novell file server and access network resources. When a client computer requires network resources, the client software communicates with the server using an appropriate communication protocol. Requests for network resources take the form of a system call to the client software. The request is forwarded (redirected) to an available network server by a software component called a redirector. If the user has appropriate rights, the server provides the requested services or resources.