An operating system acts as an intermediary between the user of a computer and the computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient and efficient manner.
An operating system is software that manages the computer hardware. The hardware must provide appropriate mechanism to ensure the correct operation of the computer system and to prevent user programs from interfering with the proper operation of the system.
Internally, operating systems vary greatly in their markup, since they are organized along many different lines. The design of a new operating system is a major task. It is important that the goals of the system be well defined before the design begins. These goals form the basis for choices among various algorithms and strategies.
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.
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 system is how varied they are in accomplishing these tasks. Mainframe operating systems are designed primarily to optimized 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 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.
- To provide a grand tour of the major components of operating systems.
- To determine the basic organization of computer systems.
What Operating System Do
We begin our discussion by looking the operating system’s role in the overall computer system. A computer system can be divided roughly into four components: the hardware, the operating system, the application programs and the users.
The hardware- the central processing unit (CPU), the memory, and the input/output (I/O) devices- provides the basic computing resources for system. The application programs- such as word processors, spreadsheets, compilers, and Web browsers-define the ways in which these resources are used to solve user’s, computing problems. The operating system controls the hardware and coordinates its use among the various application programs for various users.
We can also view a computer system as consisting of hardware, software, and data. The operating system provides the means for proper use of these resources in the operation of the computer system. An operating system is similar to a government. Like a government it performs no useful function by itself. It simply provide an environment within which other programs can do useful work.
To understand more fully the operating system’s role, we next explore operating systems from two viewpoints: that one of the user and that of the system.
The user view of the computer varies according to the interface being used. Most computer users sit in front of a PC, consisting of a monitor, keyboard, mouse, and system unit. Such a system is designed for one user to monopolize its resources. The goal is to maximize the work (or play) that user is performing. In this case, the operating system is designed mostly for ease of use, with some attention paid to performance and non paid to resource utilization-how various hardware and software resources are shared. Performance is, of course, important to the user; but such systems are optimized for the single-user experience rather than the requirements of multiple users.
In other cases, a user sits at a terminal connected to a mainframe or minicomputer. Other user are accessing the same computer through other terminals. These uses 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 services—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 theses are standalone units for individuals users. Some are connected are 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 unit of battery life is important as well.
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