Unit 1

Introduction to OS

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Topic
s• Introduction: Definition of Operating system
• Operating System’s role
• Operating-System Operations
• Functions of Operating System
• Computing Environments

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 Introductio
•n
It is a software that works as an interface between a user and the
computer hardware.
• An operating system acts as an intermediatry between the user of
a computer and computer hardware.
• The purpose of an operating system is to provide an environment
in which a user can execute programs in a convenient and efficient
manner.
• The primary objective of an operating system is to make computer
system convenient to use and to utilize computer hardware in an
efficient manner.
• The operating system performs the basic tasks such as receiving
input from the keyboard, processing instructions and sending
output to the screen.
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• An Operating System (OS) is an interface between a computer
user and computer hardware. An operating system is a software
which performs all the basic tasks like file management, memory
management, process management, handling input and output,
and controlling peripheral devices such as disk drives and
printers.
• Some popular Operating Systems include Linux Operating
System, Windows Operating System, VMS, OS/400, AIX, z/OS,
etc.

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History of Operating system

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 Components of a computer system
• Hardware – provides basic computing resources CPU,
memory, I/O devices
• Operating system-Controls and coordinates use of
hardware among various applications and users
• Application programs – define the ways in which the system
resources are used to solve the computing problems of the
users
-Word processors, compilers, web browsers, database
systems, video games
• Users
- People, machines, other computers 6
Abstract view of the components of a computer system. 7
• The operating system manages a computer's software
hardware resources, including:
⮚Input devices such as a keyboard and mouse.
⮚Output devices such as display monitors, printers and scanners.
⮚Network devices such as modems, routers and
network connections.
⮚Storage devices such as internal and external drives.
• The OS also provides services to facilitate the efficient
execution and management of, and memory allocations for, any
additional installed software application programs.

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OS is designed to serve two basic purposes:

1.It controls the allocation and use of the computing System’s

resources among the various user and tasks.
2.It provides an interface between the computer hardware and the
programmer that simplifies and makes feasible for coding,
creation, debugging of application programs.

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The Operating system must support the following tasks. The
task are:
1.Provides the facilities to create, modification of programs and
data files using an editor.
2.Access to the compiler for translating the user program from high
level language to machine language.
3.Provide a loader program to move the compiled program code to
the computer’s memory for execution.
4. Provide routines that handle the details of I/O programming.

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Two Views of Operating System
1.User's View
2.System View
1. Operating System: User View
• The user view of the computer refers to the interface being used. Such
systems are designed for one user to monopolize its resources, to
maximize the work that the user is performing. In these cases, the
operating system is designed mostly for ease of use, with some attention
paid to performance, and none paid to resource utilization.

2. Operating System: System View

• Operating system can be viewed as a resource allocator also. A computer
system consists of many resources like - hardware and software - that
must be managed efficiently. The operating system acts as the manager
of the resources, decides between conflicting requests, controls execution
of programs etc.
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Functions of an Operating System

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Types of Operating system

⮚Batch Operating System

⮚Multitasking/Time Sharing
OS
⮚Multiprocessing OS
⮚Real Time OS
⮚Distributed OS
⮚Network OS
⮚Mobile OS

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Batch
OS
• This type of operating system
does not interact with the
computer directly. There is an
operator which takes similar
jobshaving same
requirement and group them
into batches. It is the
responsibility of operator to
sort the jobs with similar
needs.

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 Advantages and
Disadvantage
Advantages Disadvantages
• It is very difficult to guess or know • The computer operators
the time required by any job to should be well known with
complete. Processors of the batch batch systems
systems know how long the job
would be when it is in queue • Batch systems are hard to
• Multiple users can share the batch debug
systems • It is sometime costly
• The idle time for batch system is
very less • The other jobs will have to
• It is easy to manage large work wait for an unknown time if
repeatedly in batch systems any job fails
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Time-Sharing Operating Systems
• Each task is given some time to
execute, so that all the tasks
work smoothly. Each user gets
time of CPU as they use single
system. These systems are also
known as Multitasking Systems.
The task can be from single
user or from different users also.
The time that each task gets to
execute is called quantum. After
this time interval is over OS
switches over to next task.

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Advantages and
Disadvantage
Advantages Disadvantages
• Each task gets an equal • Reliability problem
opportunity • One must have to take care of
security and integrity of user
• Less chances of duplication
programs and data
of software
• Data communication problem
• CPU idle time can be reduced

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Multiprogramming Operating Systems
• Sharing the processor, when
two or more programs reside
in memory at the same time,
is referred
as multiprogramming.
• Multiprogramming assumes a
single shared processor.
Multiprogramming increases
CPU utilization by organizing
jobs so that the CPU always
has one to execute.

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Advantages and
Disadvantage
Advantages Disadvantages
• High and efficient • CPU scheduling is required.
CPU utilization. • To accommodate many
jobs in memory, memory
• User feels that many
management is required.
programs are allotted CPU
almost simultaneously.

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Distributed Operating System
• Multiple central processors are used by
Distributed systems to serve multiple real-time
applications and multiple users. Accordingly,
Data processing jobs are distributed among
the processors.

• Processors communicate with each other

through various communication lines (like
high-speed buses or telephone lines). These
are known as loosely coupled systems or
distributed systems. Processors in this system
may vary in size and function. They are
referred as sites, nodes, computers, and so
on.

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Advantages and
Disadvantage
Advantages Disadvantages
• Failure of one will not affect the other
network communication, as all systems
• Failure of the main network will
are independent from each other stop the entire communication
• Electronic mail increases the data • To establish distributed systems
exchange speed the language which are used
• Since resources are being shared,
computation is highly fast and durable
are not well defined yet
• Load on host computer reduces • These types of systems are not
• These systems are easily scalable as readily available as they are
many systems can be easily added to the very expensive. Not only that
network the underlying software is highly
• Delay in data processing reduces complex and not understood
well yet
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Network Operating System
These systems run on a server and
provide the capability to manage data,
users, groups, security, applications,
and other networking functions.
• These type of operating systems allow
shared access of files, printers,
security, applications, and other
networking functions over a small
private network.
• These computers are popularly known
as tightly coupled systems.

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Advantages and
Disadvantage
Advantages Disadvantages
• Highly stable centralized • Servers are costly
servers
• User has to depend on
• Security concerns are handled
through servers central location for most
operations
• New technologies and hardware
up-gradation are easily • Maintenance and updates are
integrated to the system required regularly
• Server access are possible
remotely from different locations
and types of systems
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 Real-Time Operating System
• These types of OSs serves the real-time systems. The time interval required to process and
respond to inputs is very small. This time interval is called response time.
• In a RTOS, Processing time requirement are calculated in tenths of seconds increments of
time. It is time-bound system that can be defined as fixed time constraints.
• Real-time systems are used when there are time requirements are very strict like missile
systems, air traffic control systems, robots etc.

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Advantages and
Disadvantage
Advantage Disadvantages
•s Maximum Consumption: Maximum utilization of • Limited Tasks: Very few tasks run at the
devices and system, thus more output from all the same time and their concentration is very less
resources on few applications to avoid errors.
• Task Shifting: Time assigned for shifting tasks in these
systems are very less. For example in older systems it • Use heavy system resources: Sometimes
takes about 10 micro seconds in shifting one task to the system resources are not so good and they
another and in latest systems it takes 3 micro seconds. are expensive as well.
• Focus on Application: Focus on running applications • Complex Algorithms: The algorithms are very
and less importance to applications which are in queue.
• Real time operating system in embedded complex and difficult for the designer to write
system: Since size of programs are small, RTOS can
also be used in embedded systems like in transport and on.
others.
• Error Free: These types of systems are error free. • Device driver and interrupt signals: It needs
• Memory Allocation: Memory allocation is best specific device drivers and interrupt signals to
managed in these type of systems.
response earliest to interrupts.
• Thread Priority: It is not good to set thread
priority as these systems are very less prone
to switching tasks. 25
Mobile OS
• A mobile operating system, also called a mobile OS, is an
operating system that is specifically designed to run on mobile
devices such as mobile phones, smartphones, PDAs, tablet
computers and other handheld devices

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Types of Mobile OS
• Android OS (Google Inc.)
• Bada (Samsung Electronics)
• BlackBerry OS (Research In Motion)
• iPhone OS / iOS (Apple)
• MeeGo OS (Nokia and Intel)
• Palm OS (Garnet OS)
• Symbian OS (Nokia)

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 Operating System Operations
• Operating Systems are interrupt driven. The interrupt is a signal emitted by hardware
or software when a process or an event needs immediate attention. It alerts the
processor to a high-priority process requiring interruption of the current working
process.

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Interrupts:
● Software Interrupts: A sort of interrupt called a software interrupt is one that is
produced by software or a system as opposed to hardware. Traps and exceptions are
other names for software interruptions. They serve as a signal for the operating
system or a system service to carry out a certain function or respond to an error
condition.
● Hardware Interrupts: A hardware interrupt is a condition related to the state of the
hardware that may be signaled by an external hardware device, e.g., an interrupt
request (IRQ) line on a PC, or detected by devices embedded in processor logic to
communicate that the device needs attention from the operating system. For example,
pressing a keyboard key or moving a mouse triggers hardware interrupts that cause
the processor to read the keystroke or mouse position.
Computing Environments
Traditional Computing - In traditional computing the user can use a
traditional method like static memory allocation and it is mainly useful in single user
operating systems.
In this technique there will be a particular operating system that is going to perform all tasks
to that particular computer system.
It is like one task is performed by the CPU at a given time and the CPU utilizes the memory
that is used only for one task.

Client-Server Computing - In client-server computing there is a

technology available by using a client and server that are connected with each other with
the help of a network. When some process or program transfers from client to server or
server to client then the memory and I/O calculations is called client-server computing.
Basically in the internet the user can use this technology and a network is used to connect
the server with the client. So, that the client and server are connected with each other for
client-server computing.
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Computing Environments
Peer-to-Peer Computing - In Peer to Peer computing a node first joins the
network and a number of nodes are directly connected to the network, so every single node
has a direct connection with all the other nodes and this type of computing is called Peer to
Peer computing.
The Peer to Peer network is a network which is based on specific tasks and it is a centralized
service where one single node will be connected to all the other nodes just like our
computer where CPU is connected to all resources to perform operation.

Cloud computing
Cloud computing is a type of computing which delivers computing storage and services
across the network.
All the data is stored in cloud computing because it can be used by different servers to store
their data and use whenever they want.
In cloud computing different types of servers are used and storage manager is used to
manage the computing and there will be cloud management service through which
different companies are directly connected with it and store their data.
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