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Unit 1: Introduction to Operating System

not run, eliminating the possibility of outside interference. On some systems a lost superuser Notes
password can be changed by switching to single user mode, but not asking for the password in
such circumstances is viewed as a security vulnerability.
You are all familiar with the concept of sitting down at a computer system and writing documents
or performing some task such as writing a letter. In this instance, there is one keyboard and one
monitor that you interact with.
Operating systems such as Windows 95, Windows NT Workstation and Windows 2000
professional are essentially single user operating systems. They provide you the capability to
perform tasks on the computer system such as writing programs and documents, printing and
accessing fi les.
Consider a typical home computer. There is a single keyboard and mouse that accept input
commands, and a single monitor to display information output. There may also be a printer for
the printing of documents and images.
In essence, a single-user operating system provides access to the computer system by a single
user at a time. If another user needs access to the computer system, they must wait till the current

user finishes what they are doing and leaves.
Students in computer labs at colleges or University often experience this. You might also have
experienced this at home, where you want to use the computer but someone else is currently

using it. You have to wait for them to finish before you can use the computer system.
1.4 Goals of an Operating System

The primary objective of a computer is to execute an instruction in an efficient manner and to
increase the productivity of processing resources attached with the computer system such as
hardware resources, software resources and the users. In other words, you can say that maximum
CPU utilisation is the main objective, because it is the main device which is to be used for the
execution of the programs or instructions. Brief the goals as:
1. The primary goal of an operating system is to make the computer convenient to use.
2. The secondary goal is to use the hardware in an effi cient manner.

1.5 Generations of Operating Systems

Operating systems have been evolving over the years. you will briefly look at this development
of the operating systems with respect to the evolution of the hardware/architecture of the
computer systems in this section. Since operating systems have historically been closely tied with
the architecture of the computers on which they run, you will look at successive generations of
computers to see what their operating systems were like. You may not exactly map the operating
systems generations to the generations of the computer, but roughly it provides the idea behind
them.
You can roughly divide them into five distinct generations that are characterized by hardware

component technology, software development, and mode of delivery of computer services.

1.5.1 0 Generation
th
The term 0 generation is used to refer to the period of development of computing, which predated
th
the commercial production and sale of computer equipment. You consider that the period might
be way back when Charles Babbage invented the Analytical Engine. Afterwards the computers
by John Atanasoff in 1940; the Mark I, built by Howard Aiken and a group of IBM engineers
at Harvard in 1944; the ENIAC, designed and constructed at the University of Pencylvania by

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