Page 42 - DCAP103_Principle of operating system

Unit 1: Operating System

network (MAN), could link buildings within a city. BlueTooth devices communicate over a Notes
short distance of several feet, in essence creating a small-area network.
The media to carry networks are equally varied. They include copper wires, fiber strands, and
wireless transmissions between satellites, microwave dishes, and radios. When computing
devices are connected to cellular phones, they create a network. Even very short-range infrared
communication can be used for networking. At a rudimentary level, whenever computers
communicate they use or create a network. These networks also vary by their performance
and reliability.
1.11.1 Client-Server Systems

As PCs have become faster, more powerful, and cheaper, designers have shifted away from
the centralized system architecture. Terminals connected to centralized systems are now being
supplanted by PCs. Correspondingly, user-interface functionality that used to be handled directly
by the centralized systems is increasingly being handled by the PCs. As a result, centralized
systems today act as server systems to satisfy requests generated by client systems. The general
structure of a client-server system is depicted in Figure Server systems can be broadly categorized
as compute servers and fileservers.
Compute-server systems provide an interface to which clients can send requests to perform an
action, in response to which they execute the action and send back results to the client.
File-server systems provide a file-system interface where clients can create, update, read, and
delete files.
1.11.2 Peer-to-Peer Systems

The growth of computer networks—especially the Internet and World Wide Web (WWW)—has
had a profound influence on the recent development of operating systems. When PCs were
introduced in the 1970s, they were designed for “personal” use and were generally considered
standalone computers. With the beginning of widespread public use of the Internet in the
1980s for electronic mail, 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
component of a computer system.

Figure 1.12: General Structure of a Client-server System

Virtually 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 a local-area network or telephone connection.
Several include the web browser itself, as well as electronic mail, remote login, and file-
transfer clients and servers.

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