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Network Operating Systems
The PCs in a network must have special system software that enables them to function in a networking environment. The early network operating systems were really add-on packages that supplied the networking software for existing operating systems, such as MS-DOS or OS/2. More recent operating systems, such as Windows 95 and Windows NT, come with the networking components built in.

Client and server machines require specific software components. A computer that is in a peer-to-peer network is functioning as both a client and a server and thus requires both client and server software. Operating systems, such as Windows NT, include dozens of services and utilities that facilitate networking. You learn about some of those components in other chapters, and some are beyond the scope of the Networking Essentials exam. (You’ll get to know them when you study for the Windows NT Server or Windows NT Workstation exam.) This section introduces you to a pair of key network services —the redirector and the server—that are at the core of all networking functions.

A network client must have a software component called a redirector. In a typical stand-alone PC, I/O requests pass along the local bus to the local CPU. The redirector intercepts I/O requests within the client machine and checks whether the request is directed toward a service on another computer. If it is, the redirector directs the request toward the appropriate network entity. The redirector enables the client machine to perform the following tasks:

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In some operating environments, the redirector is called the requester. The Workstation service acts as a redirector on Windows NT systems.

A network server machine must have a component that accepts I/O requests from clients on the network and fulfills those requests by routing the requested data back across the network to the client machine. In Windows NT, the Server service performs the role of fulfilling client requests.