About operating system

Operating System

An operating system is a program that manages the computer hardware. It

also provides a basis for application programs and acts as an intermediary

between the computer user and the computer hardware. An amazing aspect

of operating systems is how varied they are in accomplishing these tasks.

Mainframe operating systems are designed primarily to optimize utilization

of hardware. Personal computer (PC) operating systems support complex

games, business applications, and everything in between. Operating systems

for handheld computers are designed to provide an environment in which a

user can easily interface with the computer to execute programs. Thus, some

operating systems are designed to be convenient, others to be efficient, and others

some combination of the two.

Before we can explore the details of computer system operation, we need

to know something about system structure. We begin by discussing the basic

functions of system startup, I/O, and storage. We also describe the basic

computer architecture that makes it possible to write a functional operating

system.

Because an operating system is large and complex, it must be created

piece by piece. Each of these pieces should be a well-delineated portion of the

system, with carefully defined inputs, outputs, and functions. In this chapter we

provide a general overview of the major components of an operating system.

In other cases, a user sits at a terminal connected to a mainframe or

minicomputer. Other users are accessing the same computer through other

terminals. These users share resources and may exchange information. The

operating system in such cases is designed to maximize resource utilization—

to assure that all available CPU time, memory, and I/O are used efficiently and

that no individual user takes more than her fair share.

In still other cases, users sit at workstations connected to networks of

other workstations and servers. These users have dedicated resources at their

disposal, but they also share resources such as networking and servers—file,

compute, and print servers. Therefore, their operating system is designed to

compromise between individual usability and resource utilization.

Recently, many varieties of handheld computers have come into fashion.

Most of these devices are standalone units for individual users. Some are

connected to networks, either directly by wire or (more often) through wireless

modems and networking. Because of power, speed, and interface limitations,

they perform relatively few remote operations. Their operating systems are

designed mostly for individual usability, but performance per amount of

battery life is important as well.

Some computers have little or no user view. For example, embedded

computers in home devices and automobiles may have numeric keypads and

may turn indicator lights on or off to show status, but they and their operating

systems are designed primarily to run without user intervention.