Operating System

Computer
Computer Fundamentals:
Fundamentals: Pradeep
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Chapter 14
Operating Systems
Ref Page Chapter 14: Operating Systems Slide 1/54

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Learning Objectives
In this chapter you will learn about:

§ Definition and need for operating system
§ Main functions of an operating system
§ Commonly used mechanisms for:
§ Process management
§ Memory management
§ File management
§ Security
§ Command interpretation module
§ Some commonly used OS capability enhancement software
§ Some popular operating systems
Ref Page 251 Chapter 14: Operating Systems Slide 2/54

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Definition and Need for OS
§ Integrated set of programs that controls the resources

(the CPU, memory, I/O devices, etc.) of a computer
system
§ Provides its users with an interface or virtual machine
that is more convenient to use than the bare machine
§ Two primary objectives of an OS are:
§ Making a computer system convenient to use
§ Managing the resources of a computer system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Logical
Logical Architecture
Architecture of
of a
a Computer
Computer System
System
Users
Other
System Software and
Application Programs
Operating System
The operating system

Computer layer hides the details of
Hardware
the hardware from the
programmer and
provides the programmer
with convenient interface
for using the system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Main Functions of an OS
§ Process management
§ Memory management
§ File management
§ Security
§ Command interpretation

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Parameters
Parameters for
for Measuring
Measuring System
System
Performance
Performance
§ Throughput: Amount of work that the system is able to

do per unit time
§ Turnaround time: Interval from the time of submission
of a job to the system for processing to the time of
completion of the job
§ Response time: Interval from the time of submission of a
job to the system for processing to the time the first
response for the job is produced by the system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Process Management
§ A process (also called job) is a program in execution

§ Process management manages the processes
submitted to a system in a manner to minimize idle time
of processors (CPUs, I/O processors, etc.) of the system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Process
Process Management
Management Mechanisms
Mechanisms in
in
Early
Early Systems
Systems
§ Manual loading mechanism: Jobs were manually

loaded one after another in a computer by the
computer operator
§ Batch processing mechanism: Batch of jobs was
submitted together to the computer and job-to-job
transition was done automatically by the operating
system
§ Job Control Language (JCL): Control statements
were used to facilitate job loading and unloading

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Use
Use of
of Job
Job Control
Control Statements
Statements in
in Batch
Batch
Processing
Processing (An
(An Example)
Example)
$END
Data for program
$RUN
$LOAD
COBOL program
$COBOL
$JOB, ONGC05839,
USER=SINHA

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming
§ Uniprogramming: Only one job is processed at a

time and all system resources are available exclusively
for the job until its completion
§ Multiprogramming: Interleaved execution of two or
more different and independent programs by a
computer
§ Types of Multiprogramming:
§ Multiprogramming with fixed tasks (MFT): Fixed
number of jobs can be processed concurrently
§ Multiprogramming with variable tasks (MVT):
Number of jobs can vary
§ Area occupied by each job residing simultaneously in
the main memory is known as a memory partition

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Job
§ CPU bound: Mostly perform computations with little

I/O operations. Scientific and engineering
computations usually fall in this category
§ I/O bound: Mostly perform I/O operations with little
computation. Commercial data processing applications
usually fall in this category

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Uniprogramming System
Main memory
Operating OS area
system
User job User program area
Execution in
progress
CPU
Only one job is processed by the system at a time and all

the system resources are exclusively available for the job
until it completes

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming System
Main memory
Operating system
Writing output data Job A
Job B
Job C
Secondary disk storage (Waiting for CPU)
Execution in
progress
CPU

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Process
Process States
States in
in Multiprogramming
Multiprogramming
Job is allocated the

New CPU for execution Job
job Ready Running processing
completed
I/O completed Job must wait for I/O

Blocked completion

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Requirements
Requirements of
of Multiprogramming
Multiprogramming Systems
Systems
§ Large memory
§ Memory protection
§ Job status preservation
§ Proper job mix (CPU and I/O bound jobs)
§ CPU scheduling

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Process
Process Control
Control Block
Block (PCB)
(PCB)
process identifier
process state
program counter
values of various CPU
registers
accounting and scheduling
information
I/O status information
PCB is used to preserve the job status of each loaded

process in a multiprogramming system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multitasking
§ Interleaved execution of multiple jobs (often referred

to as tasks of same user) in a single-user system
§ Computer systems used for multitasking are
uniprocessor systems (having only one CPU)
§ Treated differently from multiprogramming that refers
to interleaved execution of multiple jobs in a multi-
user system

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multithreading
§ Thread is basic unit of CPU utilization. Threads

share a CPU in the same way as processes do
§ All threads of a process also share the same set of
operating system resources
§ All threads of a process inherit parent’s address
space and security parameters
§ Each thread of a process has its own program
counter, its own register states, and its own stack
§ Referred as mini-process or lightweight process

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multithreading System
Address space
Address space
Thread
Thread Thread Thread
(a) Single-threaded and (b) multithreaded processes. A

single-threaded process corresponds to a process of a
traditional operating system. [Reproduced with
permission, from the book titled Distributed Operating
Systems: Concepts and Design by Pradeep K. Sinha.
© 1997 IEEE, USA].

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprocessing
§ System with two or more CPUs having ability to execute

multiple processes concurrently
§ Multiple CPUs are used to process either instructions from
different and independent programs or different
instructions from the same program simultaneously
§ Types of multiprocessing:
§ Tightly-coupled: Single system-wide primary memory
shared by all processors
§ Loosely-coupled: Each processor has its own local
memory

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
CPU,
CPU, Memory,
Memory, and
and I/O
I/O Processors
Processors of
of a
a
Computer
Computer System
System
Main
memory
I/O Units I/O

CPU
Processors

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprocessing
Multiprocessing System
System
Main
CPU-1 CPU-2
memory
I/O I/O
processors processors
I/O units I/O units

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Time-sharing
Time-sharing
§ Simultaneous interactive use of a computer system by

many users in such a way that each one feels that
he/she is the sole user of the system
§ User terminals connected to the same computer
simultaneously
§ Uses multiprogramming with a special CPU scheduling
algorithm
§ Short period during which a user process gets to use
CPU is known as time slice, time slot, or quantum
§ CPU is taken away from a running process when the
allotted time slice expires

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Process
Process State
State Diagram
Diagram for
for a
a Time-Sharing
Time-Sharing
System
System
Job is allocated to
Job
New CPU for execution Running
Ready processing
Job
completed
Allotted time slice is over
I/O completed Job must wait
for I/O
completion
Blocked

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Advantages
Advantages of
of Time-sharing
Time-sharing Systems
Systems
§ Reduces CPU idle time

§ Provides advantages of quick response time
§ Offers good computing facility to small users

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Memory
Memory Management
Management
§ Memory is important resource of a computer system

that must be properly managed for the overall system
performance
§ Memory management module:
§ Keeps track of parts of memory in use and parts not
in use
§ Allocates memory to processes as needed and
deallocates when no longer needed

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Uniprogramming
Uniprogramming Memory
Memory Model
Model
§ Used in systems that process one job only at a time, and

all system resources are available exclusively for the job
until it completes
§ Simple and easy to implement
§ Does not lead to proper utilization of the main memory as
unoccupied memory space by the currently active user
process remains unused
§ Used only on very small or dedicated computer systems

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Uniprogramming
Uniprogramming Memory
Memory Model
Model
Operating system area Operating system
User process
User area
Unused

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming
Multiprogramming Memory
Memory Models
Models
Two memory management schemes used to facilitate this

are:
§ Multiprogramming with fixed number of memory

partitions: User area of the memory is divided into a
number of fixed-sized partitions
§ Multiprogramming with variable number of memory
partitions: Number, size and location of the partitions
vary dynamically as processes come and go

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming
Multiprogramming with
with Fixed
Fixed Number
Number of
of Memory
Memory
Partition
Partition
Operating system Operating

area system
Partition 1
Partition 2
User area divided

into n equal-sized Partition 3
partitions
Partition n

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming
with Variable
Variable Number
Number of
of
Memory
Memory Partitions
Partitions
Time
Operating Operating Operating Operating
system system system system
P1 P1 P1
P1 P2 P3
comes comes comes
P2 P2
User
Free
area Free
P3
Free
Free
(a) (b) (c) (d)

The number, size, and location of the partitions vary
dynamically as processes come and go. (contd…)

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Multiprogramming
with Variable
Variable Number
Number of
of
Memory
Memory Partitions
Partitions
Operating Operating Operating Operating

system system system system
P5
P1 P1 Free 3
P4 Free 3
P2 P1 P5
P2
Comes which P4
terminates terminates P4 comes P4
cannot fit in
Free 2 which can
Free 1 so is
allocated fit in
Free 2 Free 2 Free 3 Free 2
space from
Free 2
P3 P3 P3 P3
Free 1 Free 1 Free 1 Free 1
(e) (f) (g) (h)
The number, size, and location of the partitions vary dynamically as processes come and go.

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Virtual Memory
Memory management scheme that allows execution of

processes that might not be completely loaded in the main
memory.
It does not require the entire process to be in memory

before the process can execute

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Virtual Memory Realization
Three basic concepts used for its realization are:

§ On-line secondary storage: Used to keep a process’s
address space ready to be loaded into the memory
§ Swapping: Process of transferring a block of data from
the on-line secondary storage to main memory
(swapping in) or vice-versa (swapping out)
§ Demand paging: Scheme of swapping in of pages of a
process as and when needed during execution of the
process, rather than loading all the pages before
starting the process’s execution

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Advantages of Virtual Memory
§ Provides a large virtual memory to programmers on a

system having smaller physical memory
§ Enables execution of a process on a system whose main
memory size is less than the total memory required by the
process
§ Enables a process’s execution to be started even when
sufficient free memory for loading the entire process is not
available
§ Makes programming easier there no longer need to worry
about the memory size limitations
§ Often leads to less I/O activity resulting in better
throughput, turnaround time, and response time

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Disadvantages
Disadvantages of
of Virtual
Virtual Memory
Memory
§ Difficult to implement because it requires algorithms to

support demand paging
§ If used carelessly, it may substantially decrease
performance due to high page fault rate

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File Management
§ A file is a collection of related information

§ Every file has a name, its data and attributes
§ File’s name uniquely identifies it in the system and is used
by its users to access it
§ File’s data is its contents
§ File’s attributes contain information such as date & time of
its creation, date & time of last access, date & time of last
update, its current size, its protection features, etc.
§ File management module of an operating system takes
care of file-related activities such as structuring,
accessing, naming, sharing, and protection of files

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File Access Methods
Two commonly supported file access methods are:

§ Sequential access: Information stored in a file can be
accessed sequentially (in the order in which they are
stored, starting at the beginning)
§ Random access: Information stored in a file can be
accessed randomly irrespective of the order in which
the bytes or records are stored

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File Operations
§ Set of commands provided by an operating system to

deal with files and their contents
§ Typical file operations include create, delete, open,
close, read, write, seek, get attributes, set attributes,
rename, and copy

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File Naming
File naming deals with the rules for naming files in an

operating system. This may include such rules as:
§ Maximum number of characters that a file name may
have
§ Special characters allowed in a file name
§ Distinction between upper case and lower case letters
§ Multi-part file names allow file extensions to be part of a
file name. File extensions indicate something about the
file and its content
§ Used by applications to check for the intended type of
file before operating on it

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File
File Extensions
Extensions (Example)
(Example)
File extension Its meaning
.bas Basic source program file
.c C source program file

.ftn Fortran source program file
.pas Pascal source program file
.obj Object file (compiler output, not yet linked)
.bin Executable binary program file

.lib Library of .obj files used by the linker
.dat Data file
.hlp Text file for HELP command
.man Online manual page file
(Continued on next slide)

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
File
File Extensions
Extensions (Example)
(Example)
(Continued from previous slide)
File extension Its meaning
.man Online manual page file
.txt General text file
.bak Backup file
.doc Microsoft word document file
.wav Microsoft windows sound file
.wk4 Lotus 1-2-3 spreadsheet file
.xls Microsoft Excel spreadsheet file
.jpg JPEG graphics file
.gif GIF graphics file

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Security
§ Deals with protecting the various resources and information

of a computer system against destruction and unauthorized
access
§ External security: Deals with securing computer against

external factors such as fires, floods, earthquakes, stolen
disks/tapes, etc. by maintaining adequate backup, using
security guards, allowing access to sensitive information to
only trusted employees/users, etc.
§ Internal security: Deals with user authentication, access
control, and cryptography mechanisms

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Security
§ User authentication: Deals with the problem of

verifying the identity of a user (person or program)
before permitting access to the requested resource
§ Access Control: Once authenticated, access control
mechanisms prohibit a user/process from accessing those
resources/information that he/she/it is not authorized to
access
§ Cryptography: Means of encrypting private information
so that unauthorized access cannot use information

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Command Interpretation
§ Provides a set of commands using which the user can give

instructions to the computer for getting some job done by
it
§ Commands supported by the command interpretation
module are known as system calls
(Continued on next slide)

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Command Interpretation
(Continued from previous slide)
Two types of user interfaces supported by various operating

systems are:
§ Command-line interface: User gives instructions to
the computer by typing the commands
§ Graphical User Interface (GUI): User gives
commands to the system by selecting icon or menu
item displayed on the screen with the use of a point-
and-draw device

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
OS
OS Capability
Capability Enhancement
Enhancement Software
Software
§ Perform several tasks of routine nature, frequently

needed by users but are not provided as part of the OS
§ They are primarily grouped into three categories:

§ Translating programs: Translate a source program
into an object program
§ Library programs: Consist of frequently used
functions and operations
§ Utility programs: Assist users with system
maintenance tasks such as disk formatting, data
compression, data backups, antivirus utilities

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
UNIX
UNIX OS
OS
§ Developed in the early 1970s at Bell Laboratories by Ken

Thompson and Dennis Ritchie
§ Written in C high-level language, hence, highly portable
§ Multi-user, time-sharing OS
§ Used on a wide variety of computers ranging from
notebook computers to super computers
§ Especially prevalent on RISC workstations such as those
from Sun Microsystems, Hewlett-Packard, IBM, and
Silicon Graphics
§ Structured in three layers – kernel, shell, and utilities

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
MS-DOS
§ Stands for Microsoft Disk Operating System.

§ Single-user OS for IBM and IBM-compatible personal
computers (PC)
§ Structured in three layers – BIOS (Basic Input Output
System), kernel, and shell
§ Very popular in the 1980s, now not in much use and
development with the launch of Microsoft Windows OS in
1990s

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Microsoft Windows
§ Developed by Microsoft to overcome limitations of MS-

DOS operating system
§ Single-user, multitasking OS
§ Native interface is a GUI
§ Designed to be not just an OS but also a complete
operating environment
§ OS of choice for most PCs after 1990

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Microsoft Windows NT
§ Multi-user, time-sharing OS developed by Microsoft

§ Designed to have UNIX-like features so that it can be
used for powerful workstations, network, and database
servers
§ Supports multiprogramming and is designed to take
advantage of multiprocessing on systems having
multiple processors
§ Native interface is a GUI
§ Built-in networking and communications features
§ Provides strict system security
§ Rich set of tools for software development

Computer
Pradeep K.
K. Sinha
Sinha &
& Priti
Priti Sinha
Sinha
Linux
§ Open-source OS enhanced and backed by thousands of

programmers world-wide
§ Multi-tasking, multiprocessing OS, originally designed to
be used in PCs
§ Name “Linux” is derived from its inventor Linus Torvalds
§ Several Linux distributions available (Red Hat, SuSE).
Difference in distribution is mostly set of tools, number
and quality of applications, documentation, support, and
service

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Computer

Ref Page Chapter 14: Operating Systems Slide 1/54

In this chapter you will learn about:

Ref Page 251 Chapter 14: Operating Systems Slide 2/54

Definition and Need for OS

§ Integrated set of programs that controls the resources

Ref Page 251 Chapter 14: Operating Systems Slide 3/54

The operating system

Ref Page 252 Chapter 14: Operating Systems Slide 4/54

Ref Page 252 Chapter 14: Operating Systems Slide 5/54

§ Throughput: Amount of work that the system is able to

Ref Page 253 Chapter 14: Operating Systems Slide 6/54

§ A process (also called job) is a program in execution

Ref Page 253 Chapter 14: Operating Systems Slide 7/54

§ Manual loading mechanism: Jobs were manually

Ref Page 253 Chapter 14: Operating Systems Slide 8/54

Ref Page 255 Chapter 14: Operating Systems Slide 9/54

§ Uniprogramming: Only one job is processed at a

Ref Page 255 Chapter 14: Operating Systems Slide 10/54

§ CPU bound: Mostly perform computations with little

Ref Page 255 Chapter 14: Operating Systems Slide 11/54

User job User program area

Only one job is processed by the system at a time and all

Ref Page 255 Chapter 14: Operating Systems Slide 12/54

Writing output data Job A

Ref Page 257 Chapter 14: Operating Systems Slide 13/54

Job is allocated the

I/O completed Job must wait for I/O

Ref Page 257 Chapter 14: Operating Systems Slide 14/54

Ref Page 257 Chapter 14: Operating Systems Slide 15/54

PCB is used to preserve the job status of each loaded

Ref Page 257 Chapter 14: Operating Systems Slide 16/54

§ Interleaved execution of multiple jobs (often referred

Ref Page 258 Chapter 14: Operating Systems Slide 17/54

§ Thread is basic unit of CPU utilization. Threads

Ref Page 258 Chapter 14: Operating Systems Slide 18/54

(a) Single-threaded and (b) multithreaded processes. A

Ref Page 259 Chapter 14: Operating Systems Slide 19/54

§ System with two or more CPUs having ability to execute

Ref Page 259 Chapter 14: Operating Systems Slide 20/54

I/O Units I/O

Ref Page 260 Chapter 14: Operating Systems Slide 21/54

I/O units I/O units

Ref Page 260 Chapter 14: Operating Systems Slide 22/54

§ Simultaneous interactive use of a computer system by

Ref Page 261 Chapter 14: Operating Systems Slide 23/54

Ref Page 261 Chapter 14: Operating Systems Slide 24/54

§ Reduces CPU idle time

Ref Page 262 Chapter 14: Operating Systems Slide 25/54

§ Memory is important resource of a computer system

Ref Page 262 Chapter 14: Operating Systems Slide 26/54

§ Used in systems that process one job only at a time, and

Ref Page 262 Chapter 14: Operating Systems Slide 27/54

Operating system area Operating system

Ref Page 263 Chapter 14: Operating Systems Slide 28/54

Two memory management schemes used to facilitate this

§ Multiprogramming with fixed number of memory

Ref Page 263 Chapter 14: Operating Systems Slide 29/54

Operating system Operating

User area divided