Operating Systems Introduction
Author: Brian Brown, 1995-2000. All rights reserved.
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SECTION ONE : Part 1

Overview
This module introduces you to the subject of operating systems. It is an introductory course that will take you approximately 30-40 hours to complete (including the exercises) depending upon your level of prior knowledge.

Learning Outcomes
At the end of this section you should be able to

• define what an operating system is
• list four functions performed by an operating system
• briefly explain the difference between a general purpose operating system and a dedicated operating system
• classify software according to either business, operating system, utility, education or entertainment categories
• identify from a list which items are input or output devices
• explain the difference between a single-user and a multi-user operating system
• classify common operating systems as either single-user or multi-user

What is an operating system?
An operating system (OS) is a collection of system programs that together control the operation of a computer system. Typical operating systems are Windows 98 and Linux. An operating system generally only runs on a specific hardware platform. For instance, Windows 98 only runs on computer systems based on Intel pentium processors. You can learn more about Windows 98 at the Microsoft Web Site.

What does an operating system do?
An operating system controls the way in which the computer system functions. In order to do this, the operating system includes programs that

• initialize the hardware of the computer system
• provide basic routines for device control
• provide for the management, scheduling and interaction of tasks
• maintain system integrity and handle errors

Where are operating systems found?
There are many types of operating systems, the complexity of which varies depending upon what type of functions are provided, and what the system is being used for. Some systems are responsible for managing many users on a network.
Other operating systems do not manage user programs at all. These are typically found in hardware devices like petrol pumps, airplanes, video recorders, washing machines and car engines. These are often referred to as dedicated operating systems.

What is a general-purpose operating system?

Windows NT Workstation is known as a general-purpose operating system. This is because it provides the ability to run a number of different programs, such as games, word processing, business applications and program development tools.

What is a program?
A program is a set of instructions that performs a task. When we talk about programming a computer or writing a computer program, we mean writing a set of instructions that the computer can execute. Developers (people who write programs) need to use special software to write programs, often called compilers.

Dedicated Operating Systems
An operating system designed for a single purpose is often called a dedicated operating system. It performs a specific purpose, such as controlling the environment in a building, controlling a petrol pump, or opening and closing an automatic door. Dedicated operating systems cannot be used to run other types of programs such as games or business software.

A simple operating system for a security control system
An operating system for a security control system (such as a home alarm system) would consist of a number of programs. One of these programs would gain control of the computer system when it is powered on, and initialize the system.

The first task of this initialize program would be to reset (and probably test) the hardware sensors and alarms. Once the hardware initialization was complete, the operating system would enter a continual monitoring routine of all the input sensors. If the state of any input sensor changed, it would branch to an alarm generation routine.

What are Input and Output devices?
Input and output devices are components that form part of the computer system. These devices are controlled by the operating system.

Input devices provide input signals such as commands to the operating system. These commands received from input devices instruct the operating system to perform some task or control its behavior. Typical input devices are a keyboard, mouse, temperature sensor, air-flow valve or door switch. In the previous example of our simple security control system, the input devices could be door switches, alarm keypad panel and smoke detector units.
Output devices are instruments that receive commands or information from the operating system. Typical output devices are monitor screens, printers, speakers, alarm bells, fans, pumps, control valves, light bulbs and sirens.

Exercise 1
Classify each of the following devices as an input or output device

Exercise 2
For a simple home security system, make a list of possible input and output devices that you think might be required.

Exercise 3
This is a Philips video recorder. Make a list of possible input and output devices that you think the operating system inside this video recorder might be required to manage.

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