Introduction to an NOS

A network operating system (NOS) is the system software designed especially for servers. You may have heard server used in several different ways, including in the terms file server, print server, and database server. Each type of server fits a particular need. In small businesses, it is not uncommon to find a single computer used as a file and print server. In large corporate networks, each server is configured to serve a specific task. More often than not, these large networks also will have multiple computers serving the same role (for example, multiple file servers).

file server

A computer that is dedicated to the task of centrally sharing files and folders for access by users.

print server

A centralized computer that manages printing of user documents to one or more printers. Print servers store documents temporarily when the printer is busy.

database server

A type of computer that maintains information records that can be added, deleted, changed, or searched. Database servers play a major role in most companies and on the Internet.

The concept behind an NOS is that it is easier to manage a centralized network than it is to manage a network that has all its resources spread out. An example of a decentralized model (one without a server) is a peer-to-peer network. In order for centralized servers to be effective, they have to be designed to meet stringent performance and reliability demands. The design criteria include:

Reliability  If a major software error or hardware failure occurs, the server will continue to function.

Scalability  As the needs of the company grow, the NOS is able to meet the demands. This may be accomplished by supporting larger and more powerful hardware and by adding additional servers that are designed to work in tandem.

Performance  The server provides optimum performance for the task it has been configured to serve, in addition to being adapted for more demanding scenarios.

Interoperability  Now more than ever, an NOS needs to be able to integrate with other devices, systems, and software platforms. In some instances, this integration may include a single point of management for all resources on the network.

Building a system that incorporates these criteria may seem easier than it really is. You have to remember that the NOS is only software. You still have to contend with hardware and other software (such as applications) that will be running on the system. In the case of Microsoft Windows NT, you should be able to run NT on any Intel- or Alpha-based computer. Does that mean that the system will run well or is stable? Not at all. You need to take into consideration the extent to which all of the hardware components have been tested. These include critical components such as network interface cards, tape backup drives, and special adapters (for example, SCSI cards).

What to Look for in an NOS

Selecting the right network operating system for your company needs is important. Although most NOSs provide some similar features, each one has unique features that should be taken into consideration. The features available in an NOS may not be the only factors you will have to consider.

All the NOSs discussed later in this chapter offer the critical features a network administrator would expect to find. These common features include the following:

Fault tolerance  Fault tolerance in a server means that it is able to recover from a hardware failure or software crash without losing any data and, ideally, without any downtime. Fault-tolerant servers support RAID storage, uninterruptible power supplies, and tape backup systems.

Multiprocessing  An NOS must be able to maintain performance under demanding loads. To accomplish a consistent level of performance on a growing network, the server will need to be able to support multiple processors. An NOS that supports multiprocessing can use two or more CPUs to process an instruction simultaneously.

Multitasking  Servers, by nature, are required to complete several tasks simultaneously. If they couldn't do that effectively, they would not be of much use on a network of a thousand users. A server capable of multitasking can juggle several actions. A powerful server can handle hundreds of tasks efficiently, and without a significant decrease in performance or stability.

Besides these features, each NOS has unique qualities that may make it a good fit for your network.

Additional features to consider include wide support for different tape backup drives, antivirus software, and RAID. Compatibility with different tape drives is critical. As your data storage needs grow, so does your demand for larger backup storage. The NOS must include support for the latest tape drive technologies. As for antivirus programs, second best doesn't cut it. With the proliferation of e-mail and web-based viruses, a robust, networkable antivirus application needs to be supported by the NOS you select. And finally, the NOS must be able to support hardware- and software-based RAID options. Fortunately, this typically is not a problem because almost all NOSs, including Apple's AppleShare IP server software, will recognize a hardware RAID solution as a hard drive.