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The grown of computer network- especially the Internet and world wide web (WWW) - has a profound influence on the recent devlopment of operating systems. When PCs were introduced in the 1970s, they were designed for "personal" use and were genrally considerd stand alone computers.With the begining of widespread public use of the Internet in the 1980s for electronicmail, ftp and gopher, many PCs became connected to computer networks With the introduction of the Web in the mid-1990s,network connectivity became an essential components of computer system.
Virtully all modern PCs and workstations are capable of running a web browser for accessing hypertext documents on the Web. Operating systems(such as Windows, OS/2, MacOS, and UNIX) now also include the system software (such as TCP/IP and PPP) that enables a computer to access the Internet via local -area network or telephone connection. Servel include the webbrowser itself, as well as electronic mail, remot login, and fil-transfer client and servers.
In contrast to the tightly coupled systems discussed in Section1.4 the computer networks used in these appllications consist of a collection of processors that do not share memory or a clock. Instead, each processor has its own local memory. The processors communicate with one another through various communication lines, such as high-speed buses or telephone lines These systems
Some operating systems have taken the concept of networks and distributed systems further than the notion of providing network connectivity. A network operating systems is an operating systems that provides features such that allows different processes on diffrent computers to exchange messages. A computer running network operating system acts autonomously from all other computers on the networks although it is aware of the networks and is able to communicate with other networked computers. A distributed operating system is less autonumous environment: The diffrent operating systems communicate closely enough to provide the illusion that only a single operating system controls the network. We cover computer networks