Network operating systems have additional network management tools and features that are designed to support access by large numbers of simultaneous users. On all but the smallest networks, NOSs are installed on powerful servers. Many users, known as clients, share these servers. Servers usually have high-capacity, high-speed disk drives, large amounts of RAM, high-speed NICs, and in some cases, multiple CPUs. These servers are typically configured to use the Internet family of protocols, TCP/IP, and offer one or more TCP/IP services.

Servers running NOSs are also used to authenticate users and provide access to shared resources. These servers are designed to handle requests from many clients simultaneously. Before a client can access the server resources, the client must be identified and be authorized to use the resource. Identification and authorization is achieved by assigning each client an account name and password. The account name and password are then verified by an authentication service to permit or deny access to the network. By centralizing user accounts, security, and access control, server-based networks simplify the work of network administration.

Servers are typically larger systems than workstations and have additional memory to support multiple tasks that are active or resident in memory at the same time. Additional disk space is also required on servers to hold shared files and to function as an extension to the internal memory on the system. Also, servers typically require extra expansion slots on their system boards to connect shared devices, such as printers and multiple network interfaces.

Another feature of systems capable of acting as servers is the processing power. Ordinarily, computers have a single CPU, which executes the instructions that make up a given task or process. In order to work efficiently and deliver fast responses to client requests, a NOS server requires a powerful CPU to execute its tasks or programs. Single processor systems with one CPU can meet the needs of most servers if the CPU has the necessary speed. To achieve higher execution speeds, some systems are equipped with more than one processor. Such systems are called multiprocessor systems. Multiprocessor systems are capable of executing multiple tasks in parallel by assigning each task to a different processor. The aggregate amount of work that the server can perform in a given time is greatly enhanced in multiprocessor systems.

Since servers function as central repositories of resources that are vital to the operation of client systems, these servers must be efficient and robust. The term robust indicates that the server systems are able to function effectively under heavy loads. It also means the systems are able to survive the failure of one or more processes or components without experiencing a general system failure. This objective is met by building redundancy into server systems. Redundancy is the inclusion of additional hardware components that can take over if other components fail. Redundancy is a feature of fault tolerant systems that are designed to survive failures and can be repaired without interruption while the systems are up and running. Because a NOS depends on the continuous operation of its server, the extra hardware components justify the additional expense.

Server applications and functions include web services using Hypertext Transfer Protocol (HTTP), File Transfer Protocol (FTP), and Domain Name System (DNS). Standard e-mail protocols supported by network servers include Simple Mail Transfer Protocol (SMTP), Post Office Protocol 3 (POP3), and Internet Messaging Access Protocol (IMAP). File sharing protocols include Sun Microsystems Network File System (NFS) and Microsoft Server Message Block (SMB).

Network servers frequently provide print services. A server may also provide Dynamic Host Configuration Protocol (DHCP), which automatically allocates IP addresses to client workstations. In addition to running services for the clients on the network, servers can be set to act as a basic firewall for the network. This is accomplished using proxy or Network Address Translation (NAT), both of which hide internal private network addresses from the Internet.

One server running a NOS may work well when serving only a handful of clients. But most organizations must deploy several servers in order to achieve acceptable performance. A typical design separates services so one server is responsible for e-mail, another server is responsible for file sharing, and another is responsible for FTP.

The concentration of network resources, such as files, printers, and applications on servers, also makes the data generated easier to back up and maintain. Rather than have these resources distributed on individual machines, network resources can be located on specialized, dedicated servers for easy access and back up.

Interactive Media Activity PhotoZoom: Server Components In this PhotoZoom, the student will view components inside a server.