Operating Systems Overview (Night Class)

By Aurelie A. Peralta

Introduction

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 a 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 optimize utilization of hardware.

Personal computer (PC) operating systems support complex games, business applications, and everything in between. Handheld computer operating systems 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.

What is an Operating System?

A computer system can be divided roughly into four components:
a. Hardware
b. Operating System
c. Application programs
d. The Users

Operating Systems can be explored from two viewpoints: the user and the system.

User view

The user view of the computer varies by 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, to maximize the work that the user is performing. In this case,the operating system is designed mostly for ease of use, with some attention paid to performance, and none paid to resource utilization.

Some users sit 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 is designed to maximize resource utilization.

Other 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.

Recently, many varieties of handheld computers have come into fashion. These devices are mostly standalone, used singly by individual users. Some are connected to networks, either directly by wire or through wireless modems. Due to power and interface limitations they perform relatively few remote operations. These 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 keypad, and may turn indicator lights on or off to show status, but mostly they and their operating systems are designed to run without user intervention.

System View

We can view an operating system as a resource allocator. A computer system has many resources - hardware and software - that may be required to solve a problem. The operating system acts as the manager of these resources.

An operating system can also be viewed as a control program that manages the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.

We have no universally accepted definition of what is part of the operating system. A simple viewpoint is that it includes everything a vendor ships when you order “the operating system”.

A more common definition is that the operating system is the one program running at all times on the computer (usually called the kernel), with all else being application programs. This is the one that we generally follow.

System Goals

It is easier to define an operating system by what it does than what it is, but even this can be tricky. The primary goal of some operating system is convenience for the user. The primary goal of other operating system is efficient operation of the computer system. Operating systems and computer architecture have influenced each other a great deal. To facilitate the use of the hardware, researchers developed operating systems. Users of the operating systems then proposed changes in hardware design to simplify them. In this short historical review, notice how identification of operating-system problems led to the introduction of new hardware features.

Mainframe Systems

Mainframe computer systems were the first computers used to tackle many commercial and scientific applications.

Assignment:
1. Batch Systems
2. Multiprogrammed Systems
3. Time-Sharing Systems

Desktop Systems

Personal Computers or PCs appeared in the 1970s. Operating Systems for PCs opt for maximizing user convenience and responsiveness.

Multiprocessor Systems

Multiprocessor systems also known as parallel systems or tightly coupled systems are growing in importance. Such systems have more than one processor in close communication, sharing the computer bus, the clock, and sometimes memory and peripheral devices.
Multiprocessor systems have three main advantages:
1. Increased throughput
2. Economy of scale
3. Increased reliability

Distributed Systems

A network, in the simplest terms, is a communication path between two or more systems. Distributed systems depend on networking for their functionality.

1. Client-Server Systems
2. Peer-to-Peer Systems

Clustered Systems

Like parallel systems, clustered systems gather together multiple CPUs to accomplish computational work. They differ from parallel systems in that they are composed of two or more individual systems coupled together. Clustering is usually performed to provide high availability.

Real-Time Systems

A real-time system is used when rigid time requirements have been placed on the operation of a processor or the flow of data thus it is often used as a control device in a dedicated application. Sensors bring data to the computer. A real-time system has well-defined, fixed time constraints. Processing must be done within the defined constraints, or the system will fail.

Handheld Systems

Handheld systems include personal digital assistants (PDAs) or cellular telephones with connectivity to a network such as the Internet.

Computing Environments
1. Traditional Computing
2. Web-Based Computing
3. Embedded Computing

 Reference: Operating System Concepts by Silberschatz, Galvin, and Gagne, 2003