A computer operating system (OS) is the software foundation on which computer applications and services run on a workstation. Similarly, a network operating system (NOS) enables communication between multiple devices and the sharing of resources across a network. A NOS operates on UNIX, Microsoft Windows NT, or Windows 2000 network servers.

Common functions of an OS on a workstation include controlling the computer hardware, executing programs and providing a user interface. The OS performs these functions for a single user. Multiple users can share the machine but they cannot log on at the same time. In contrast, a NOS distributes functions over a number of networked computers. A NOS depends on the services of the native OS in each individual computer. The NOS then adds functions that allow access to shared resources by a number of users concurrently.

Workstations function as clients in a NOS environment. When a workstation becomes a client in a NOS environment, additional specialized software enables the local user to access non-local or remote resources, as if these resources were a part of the local system. The NOS enhances the reach of the client workstation by making remote services available as extensions of the local operating system.

A system capable of operating as a NOS server must be able to support multiple users concurrently. The network administrator creates an account for each user, allowing the user to logon and connect to the server system. The user account on the server enables the server to authenticate that user and allocate the resources that the user is allowed to access. Systems that provide this capability are called multi-user systems.

A NOS server is a multitasking system, capable of executing multiple tasks or processes at the same time. The NOS scheduling software allocates internal processor time, memory, and other elements of the system to different tasks in a way that allows them to share the system resources. Each user on the multi-user system is supported by a separate task or process internally on the server. These internal tasks are created dynamically as users connect to the system and are deleted when users disconnect.

The main features to consider when selecting a NOS are performance, management and monitoring tools, security, scalability, and robustness or fault tolerance. The following section briefly defines each of these features.

Performance
A NOS must perform well at reading and writing files across the network between clients and servers. It must be able to maintain fast performance under heavy loads, when many clients are making requests. Consistent performance under heavy demand is an important standard for a NOS.

Management and monitoring
The management interface on the NOS server provides the tools for server monitoring, client administration, file, print, and disk storage management. The management interface provides tools for the installation of new services and the configuration of those services. Additionally, servers require regular monitoring and adjustment.

Security
A NOS must protect the shared resources under its control. Security includes authenticating user access to services to prevent unauthorized access to the network resources. Security also performs encryption to protect information as it travels between clients and servers.

Scalability
Scalability is the ability of a NOS to grow without degradation in performance. The NOS must be capable of sustaining performance as new users join the network and new servers are added to support them.

Robustness/fault tolerance
A measure of robustness is the ability to deliver services consistently under heavy load and to sustain its services if components or processes fail. Using redundant disk devices and balancing the workload across multiple servers can improve NOS robustness.