Chapter 2 operating systems

Unit 1
Computer Systems and Organisation (CSO)
XI
Computer Science (083)
Board : CBSE
CHAPTER 2
OPERATING SYSTEMS

Unit I
Computer Systems and Organisation (CSO)
(10 Theory + 02 Practical)
Department of Computer Science, Sainik School Amaravathinagar)
Cell :9431453730
Email : praveenkumarjigajinni@gmail.com
Prepared by
Courtesy CBSE
Praveen M Jigajinni
DCSc & Engg,PGDCA,ADCA,MSc(IT),MCA,Mtech, MPhil (CS)

Operating System
 An Operating system is the most
important system software.
It is a set of programs that control
and supervise the hardware of a
computer and also provide services to
application software, programmers
and users.

Operating System
It manages all hardware and
software, input, output and
processing activities within the
computer system, the flow of
information to and from the
processor, sets priorities for handling
different tasks, and so on.

Operating System
When a computer is switched on, the
operating system is the first program
that is loaded onto its memory.
A user cannot communicate directly
with the computer hardware, so the
operating system acts as an interface
between the user and the computer
hardware.

Operating System
Some of the popular operating
systems used in personal computers
are DOS, Windows, Unix, Linux,
Solaris, etc.

Need for an Operating System
Operating system provides a platform,
on top of which, other programs, called
application programs can run. As
discussed before, it acts as an interface
between the computer and the user.
It is designed in such a manner that it
operates, controls and executes various
applications on the computer.

It also allows the computer to manage
its own resources such as memory,
monitor, keyboard, printer etc.
Our choice of operating system,
therefore, depends to a great extent on
the CPU and the other attached devices
and the applications we want to run.

The operating system controls the
various system hardware and software
resources and allocates them to the users
or programs as per their requirement.

Functions of an Operating System
An operating system has variety of
functions to perform.
Some of the prominent functions of an
operating system can be broadly outlined
as:

Functions of an Operating System
An operating system has variety of
functions to perform. Some of the
prominent functions of an operating
system can be broadly outlined as:
Processor Management
Device Management
Memory management
File Management

Processor Management
This deals with management of the
Central Processing Unit (CPU). The
operating system takes care of the
allotment of CPU time to different
processes this is called scheduling.

Concept of Memory Map of Process
Global Variables Program Code
Heap
Stack

State of Process
RunningReadyStart
TerminateWait

The Operating System communicates
with hardware and the attached
devices and maintains a balance
between them and the CPU.
This is all the more important
because the CPU processing speed is
much higher than that of I/O devices.
I/O Device Management

In a computer, both the CPU and the
I/O devices interact with the memory.
When a program needs to be executed
it is loaded onto the main memory till
the execution is complete.
Thereafter that memory space is
freed and is available for other
programs.
Memory management

The common memory management
techniques used by the operating
system are Partitioning and Virtual
Memory.
Memory management

The total memory is divided into
various partitions of same size or
different sizes.
This helps to accommodate number
of programs in the memory.
Memory management - Partitioning

The partition can be fixed i.e. remains
same for all the programs in the
memory or variable i.e. memory is
allocated when a program is loaded on
to the memory.
The later approach causes less
wastage of memory but in due course
of time, it may become fragmented.
Memory management - Partitioning

This is a technique used by the
operating system by virtue of which the
user can load the programs which are
larger than the main memory of the
computer.
In this technique the program is
executed even if the complete program
is not loaded on to the main memory.
Memory management - Virtual Memory

In this technique the program is
executed even if the complete program
is not loaded on to the main memory.
The operating system divides the
main memory into equal sizes called
pages.

A part of the program resides in the
main memory and is called the active
set.
The rest is in the secondary storage
device in the form of tracks/sectors or
blocks.

With the help of Page Map Tables
(PMT), the operating system keeps
track which page of main memory is
storing which block of secondary
memory.

Page Map Table (PMT)

Let me talk around this a bit and hopefully
I can be of some help. First, an analogy -
imagine that you're trying to locate a house
in a city. Imagine that each house was given
a unique number - you can imagine that the
number of houses would soon get very
large and confusing.

Now imagine that you introduce the
concept of streets - the house numbers now
become a bit more managable as you've
grouped them into nice chunks. So:
Streets = Page number,
house number = offset address.

The whole point of having virtual memory
pages is to allow the computer to carve
memory up into manageable chunks and
not waste too much of it. Carving it into
chunks (pages) allows granular control of
access, paging and other nice things like
that The smaller your pages, the less
memory you're going to waste.

 (if process A requires 32k of memory, and
your page size is 64k, you're going to end up
with some which isn't used), but the higher
the overhead on the system.

A virtual address (which is not the
real physical address In computing,
a virtual address space (VAS) or address
space is the set of ranges of virtual
addresses that an operating system
makes available to a process.) is
mapped either to the main memory or
the secondary memory.

Hence virtual memory allows more
programs and even larger programs to
be executed in the main memory
leading to efficient memory utilization.

The operating System manages the
files, folders and directory systems on a
computer. Any data on a computer is
stored in the form of files and the
operating system keeps information
about all of them using File Allocation
Table (FAT).
File Management

The FAT stores general information
about files like filename, type (text or
binary), size, starting address and
access mode (sequential/indexed
sequential/direct/relative).
File Management

The file manager of the operating
system helps to create, edit, copy,
allocate memory to the files and also
updates the FAT. The operating system
also takes care that files are opened
with proper access rights to read or edit
them.
File Management

OS are classified into the following
types depending on their processing
capabilities and they are:-
Single User and Single Task OS
Multiuser OS
Multiprocessing OS
Types of Operating System

Time sharing Operating System
Real Time Operating System
Distributed Operating System
Interactive Operating System

It is used on a standalone single
computer for performing a single task.
Operating systems for Personal
Computers (PC) are single-user OS.
Single user OS are simple operating
system designed to manage one task at
a time. MS-DOS is an example of single
user OS.
Single User and Single Task OS

Multiuser OS is used in mini
computers or mainframes that allow
same data and applications to be
accessed by multiple users at the same
time.
The users can also communicate with
each other. Linux and UNIX are
examples of multiuser OS.
Multiuser OS

Multiprocessing OS have two or more
processors for a single running process.
Processing takes place in parallel and is
also called parallel processing. Each
processor works on different parts of
the same task, or, on two or more
different tasks.
Multiprocessing OS

Since execution takes place in
parallel, they are used for high speed
execution, and to increase the power of
computer. Linux, UNIX and Windows 7
are examples of multiprocessing OS.
Multiprocessing OS

Time sharing Operating System: It
allows execution of more than one
tasks or processes concurrently. For
this, the processor time is divided
amongst different tasks this division of
time is also called time sharing.
The processor switches rapidly
between various processes.
Time sharing OS

After the stipulated time is over, the
CPU shifts to next task in waiting, So
this type of operating system employs
round robin scheduling technique.
The system switches rapidly from one
user to another but still each user feels
that it is getting a dedicated CPU time.
Time sharing OS

Virtual Memory techniques are used
in this type of operating system. For
example, the user can listen to music
on the computer while writing an
article using a word processing
software.
Time sharing OS

The user can switch between the
applications and also transfer data
between them.
Time sharing operating system can be
both single user and multiuser.
Windows 95 and all later versions of
Windows are examples of multitasking
OS.
Time sharing OS

 For example a mainframe computer
that has many users logged on to it.
Each user uses the resources of the
mainframe -i.e. memory, CPU etc. The
users feel that they are exclusive user
of the CPU, even though this is not
possible with one CPU i.e. shared
among different users.
Time sharing OS

It is a multitasking operating system
designed for real time applications like
robotics. In this type of operating
system, the tasks have to be done
within a fixed deadline.
For Example
eCos, LynxOS, QNX, RTAI, RTLinux, Sy
mbian OS, VxWorks, Windows
CE,MontaVista Linux.
Real Time Operating System

System performance is good if task is
finished within this deadline. If it is not
done, the situation is called Deadline
Overrun. Lesser the deadline over run,
better is the system efficiency. Hence
Real Time operating systems depend
not only on the logical result of the
computation but also on the time in
which the results are produced.
Real Time Operating System

On a network data is stored and
processed on multiple locations.
The Distributed Operating System is
used on networks as it allows shared
data/files to be accessed from any
machine on the network in a
transparent manner.
Distributed Operating System

We can insert and remove the data
and can even access all the input and
output devices. The users feel as if all
data is available on their workstation
itself.

Examples
AEGISOS - for the Apollo DOMAIN
Distributed system. Early 1980s.
Charlotte Distributed OS for the Crystal
Multicomputer project 1989
CHOICES – OOPs based OS featuring a high
degree of customization. U. of Idaho, 1990s
DUNIX - Developed at Bell Labs. late 1980s.
SODA - A Simplified OS for Distributed
Applications. Mid 1980s.

This is the operating system that
provides a Graphic User Interface (GUI)
through which the user can easily navigate
and interact. The computer responds
almost immediately after an instruction
has been entered, and the user can enter
new instructions after seeing the results
of the previous instructions. For example
Win, Linux, Oracle Solaris etc
Interactive Operating System

Windows
Linux
BOSS (Bharat Operating System
Solutions)
UNIX
Solaris
Commonly Used Operating Systems

Microsoft Windows is a group of
several graphical operating system
families, all of which are developed,
marketed, and sold by Microsoft.
Windows

Linux is a family of free and open-
source software operating systems
built around the Linux kernel.
Typically, Linux is packaged in a form
known as a Linux distribution (or distro
for short) for both desktop and server
use.
LINUX/UNIX

This is an Indian distribution of
GNU/Linux. It consists of Linux
operating system kernel, office
application suite, Bharateeya OO,
Internet browser (Firefox), multimedia
applications and file sharing.
BOSS

It is a free Unix based operating
system introduced by Sun
Microsystems in 1992. It is now also
known as Oracle Solaris. It is quite
scalable and is used on virtual
machines.
Solaris

It is the operating system that
operates on digital mobile devices like
smart phones and tablets. It extends
the features of a normal operating
system for personal computers so as to
include touch screen, Bluetooth, WiFi,
GPS mobile navigation, camera, music
player and many more. The most
commonly used mobile operating
systems are –
Mobile Operating Systems

 BlackBerry OS, webOS, iOS,
Symbian, Android, Windows
Mobile Professional (touch screen),
Windows Mobile Standard (non-touch
screen), and Bada. The most popular
are the Apple iPhone, a mobile OS
developed by Google, is the first
completely open-source mobile OS.
Mobile Operating Systems

It is a Linux derived Mobile OS
released on 5th November 2007 and by
2011 it had more than 50% of the
global Smartphone market share. It is
Google’s open and free software that
includes an operating system,
middleware and some key applications
for use on mobile devices.
Mobile Operating Systems - Android

Android applications are quiet user
friendly and even one can easily
customize the Smartphone with
Android OS.
The Android releases have dessert
inspired codenames like Cupcake,
Honeycomb, Ice Cream sandwich and
Jelly Bean.
Mobile Operating Systems - Android

This Mobile OS by Nokia (currently
being maintained by Accenture)
designed for smartphones. It offers
high level of functional integration
between communication and personal
information management.
Mobile Operating Systems - Symbian

It has an integrated mail box and it
completely facilitates the usage of all
Google applications in your
smartphone easily.
Symbian applications are easy to shut
down as compared to Android
applications.
Mobile Operating Systems - Symbian

CLASS TEST
Time: 40 Min Max Marks: 20
1. Write a note on OS 05
2. Explain process management 05
3. Write a note on memory management
05
4. Explain the types of OS 05

Chapter 2 operating systems

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