Operating Systems unit 1 & 2 - BBA / MBA

What is an Operating System?
The most important
program that runs on your
computer. It manages all
other programs on the
machine.
Every PC has to have one
to run other applications
or programs.
It’s the first thing
“loaded”.

Operating
System
•It performs basic tasks,
such as:
• Recognizing input from the
keyboard or mouse,
• Sending output
to the monitor,

Why are Operating
Systems Used?
• Operating System is used as a
communication channel between the
Computer hardware and the user.
• It works as an intermediate between
System Hardware and End-User.

•Keeping track of files and
directories on the disk, and
•Controlling peripheral
devices such as disk drives
and printers.
Why are Operating
Systems Used?

Why are
Operating
Systems
Used?
• Operating System handles the following
responsibilities:
• It controls all the computer resources.
• It provides valuable services to user programs.
• It coordinates the execution of user programs.
• It provides resources for user programs.
• It provides an interface (virtual machine) to the
user.
• It hides the complexity of software.
• It supports multiple execution modes.
• It monitors the execution of user programs to
prevent errors.

Functions of Operating Systems
1. Memory Management
2. Process Management
3. Device Management
4. File Management
5. Security
6. GUI
7. Booting
8. Control Over System
Performance
9. Job Accounting
10. Resource Management
11. Networking
12. Backup & Recovery
13. Virtualization
14. Error – Detecting Aids
15. Time Sharing
16. System Calls

1. Memory Management
• The operating system manages the computer’s primary
memory and provides mechanisms for optimizing memory
usage.
• The operating system manages the Primary Memory or Main
Memory.
• Main memory is made up of a large array of bytes or words
where each byte or word is assigned a certain address.
• Main memory is fast storage and it can be accessed directly by
the CPU.
• For a program to be executed, it should be first loaded in the
main memory.
• An operating system manages the allocation and deallocation
of memory to various processes and ensures that the other
process does not consume the memory allocated to one
process.

• An Operating System performs the following
activities for Memory Management:
• It keeps track of primary memory, i.e., which bytes of
memory are used by which user program.
• The memory addresses that have already been allocated and
the memory addresses of the memory that has not yet been
used.
• In multiprogramming, the OS decides the order in
which processes are granted memory access, and for
how long.
• It Allocates the memory to a process when the process requests
it and deallocates the memory when the process has
terminated or is performing an I/O operation.

• A computer has different memory types it
could use; memory registers, cache, RAM
and disk storage.
• The OS is responsible for checking;
• which memory if free
• which memory is to be
• allocated and de- allocated
• how to swap between the
• main memory and secondary memory

• When the OS swaps between main memory and
secondary memory we call this Virtual Memory
management
• Virtual memory creates a memory slot acting as
RAM when the RAM is too full
• Virtual memory is much slower than RAM

2. Process Management
• The operating system is responsible for starting,
stopping, and managing processes and programs.
• It also controls the scheduling of processes and allocates
resources to them.
• In a multi-programming environment, the OS decides
the order in which processes have access to the
processor, and how much processing time each
process has.
• This function of OS is called Process Scheduling.

• An Operating System performs the following activities
for Processor Management.
• An operating system manages the processor’s work by allocating various
jobs to it and
• ensuring that each process receives enough time from the processor to function
properly.
• Keeps track of the status of processes.
• The program which performs this task is known as a traffic controller.
• Allocates the CPU that is a processor to a process. De-allocates processor
when a process is no longer required.

New State
- A process is said
to be in new state
when a program
present in the
secondary
memory is
initiated for
execution.
Ready State
- A process moves
from new state to
ready state after it
is loaded into the
main memory and
is ready for
execution.
- In ready state,
the process waits
for its execution
by the processor.
Run State
- A process moves
from ready state
to run state after
it is assigned the
CPU for execution.
Terminate
- A process moves
from run state to
terminate state
after its execution
is completed.
- After entering
the terminate
state, context
(PCB) of the
process is deleted
by the operating
system.

Block / Wait
State
- A process moves from run
state to block or wait state if
it requires an I/O operation
or some blocked resource
during its execution.
- After the I/O operation gets
completed or resource
becomes available, the
process moves to the ready
state.
Suspend Ready
State
- A process moves from ready
state to suspend ready state if a
process with higher priority has
to be executed but the main
memory is full.
- Moving a process with lower
priority from ready state to
suspend ready state creates a
room for higher priority process
in the ready state.
- The process remains in the
suspend ready state until the
main memory becomes
available.
- When main memory becomes
available, the process is brought
back to the ready state.
Suspend Wait
State
- A process moves from wait
state to suspend wait state if
a process with higher priority
has to be executed but the
main memory is full.
Moving a process with lower
priority from wait state to
suspend wait state creates a
room for higher priority
process in the ready state.
After the resource becomes
available, the process is
moved to the suspend ready
state.
After main memory becomes
available, the process is
moved to the ready state.

3. Device Management
• The operating system manages input/output
devices such as printers, keyboards, mice,
and displays.
• It provides the necessary drivers and
interfaces to enable communication between
the devices and the computer.
• An OS manages device communication via its
respective drivers.

• An Operating System performs the following activities for
Device management.
• Keeps track of all devices connected to the system.
• Designates a program responsible for every device known as the Input/Output
controller.
• Decide which process gets access to a certain device and for how long.
• Allocates devices effectively and efficiently. Deallocates devices when they are
no longer required.
• There are various input and output devices. An OS controls the working of
these input-output devices.
• It receives the requests from these devices, performs a specific task, and
communicates back to the requesting process.

4. File Management
• The operating system is responsible for
organizing and managing the file system,
including the
• creation, deletion, and manipulation of files and
directories.
• A file system is organized into directories
for efficient or easy navigation and usage.
• These directories may contain other directories
and other files.

• An Operating System performs the following activities for
File management.
• It keeps track of where information is stored, user access settings, the
status of every file, and more.
• These facilities are collectively known as the file system.
• An OS keeps track of information regarding the creation, deletion, transfer,
copy, and storage of files in an organized way.
• It also maintains the integrity of the data stored in these files, including the
file directory structure, by protecting against unauthorized access.

5. Security
• The operating system provides a secure
environment for the user, applications, and data by
implementing security policies and mechanisms
such as access controls and encryption.
• The operating system uses password protection to
protect user data and similar other techniques.
• It also prevents unauthorized access to programs
and user data.
• The operating system provides various techniques
which assure the integrity and confidentiality of
user data.

• The following security measures
are used to protect user data:
• Protection against unauthorized
access through login.
• Protection against intrusion by
keeping the firewall active.
• Protecting the system memory
against malicious access.
• Displaying messages related to
system vulnerabilities.

6. GUI
• The operating system provides a user interface that
enables users to interact with the computer system.
• This can be a Graphical User Interface (GUI), a Command-
Line Interface (CLI), or a combination of both.
• The user interacts with the computer system through
the operating system.
• Hence OS acts as an interface between the user and
the computer hardware.
• This user interface is offered through a set of
commands or a graphical user interface (GUI).
• Through this interface, the user makes interacts with
the applications and the machine hardware.

7. Booting
• The process of starting or restarting
the computer is known as booting.
• If the computer is switched off
completely and if turned on then it
is called cold booting.
• Warm booting is a process of using
the operating system to restart the
computer.

• What happens in the Process of Booting?
• Let's understand
• What happens when the computer switch is pressed?
• How does our computer get started?
• What all things go in the backend so that our
computer is ready to run the application programs?

Whenever we press the power button of our computer system, all the devices get
the power and they are initialized.
Our main memory which is responsible for holding the instructions will be
initially empty as RAM is volatile memory.
So, there will be a small set of instructions present in the non-volatile memory
called ROM.
These instructions will be passed to the CPU and the execution of instructions
takes place which will check all the hardware connected with the system.
If there are any problems with the hardware, we will get the alert by beep
sounds or even on-screen messages.
After the testing of the hardware is completed, the booting process continues
and loads the operating system.

8. Control Over System Performance
• Operating systems play a pivotal role in controlling and
optimizing system performance.
• They act as intermediaries between hardware and
software, ensuring that computing resources are
efficiently utilized.
• One fundamental aspect is resource allocation, where the
OS allocates CPU time, memory, and I/O devices to
different processes, striving to provide fair and optimal
resource utilization.
• Process scheduling, a critical function, helps decide
which processes or threads should run when preventing
any single task from monopolizing the CPU and enabling
effective multitasking.

9. Job Accounting
• It keeps track of time and resources used by
various jobs or users.
• The operating system Keeps track of time and
resources used by various tasks and users,
this information can be used to track
resource usage for a particular user or group
of users.
• In a multitasking OS where multiple
programs run simultaneously, the OS
determines which applications should run in
which order and how time should be
allocated to each application.

10. Resource Management
• The operating system manages and
allocates memory, CPU time, and other
hardware resources among the various
programs and processes running on the
computer.
• Coordination Between Other Software and
Users
• Operating systems also coordinate and
assign interpreters, compilers, assemble
rs, and other software to the various users
of the computer systems.

• In simpler terms, think of the operating system as the traffic cop of
your computer.
• It directs and manages how different software programs can share
your computer’s resources without causing chaos.
• It ensures that when you want to use a program, it runs smoothly
without crashing or causing problems for others.
• So, it’s like the friendly officer ensuring a smooth flow of traffic on a
busy road, making sure everyone gets where they need to go without
any accidents or jams.

11. Networking
• The operating system provides
networking capabilities such as
• establishing and managing network
connections,
• handling network protocols, and
• sharing resources such as printers
and files over a network.

• Network Communication:
• Think of them as traffic cops for your internet traffic. Operating
systems help computers talk to each other and the internet.
• They manage how data is packaged and sent over the network,
making sure it arrives safely and in the right order.
• Settings and Monitoring:
• Think of them as the settings and security guard for your
internet connection.
• They also let you set up your network connections, like Wi-Fi
or Ethernet, and keep an eye on how your network is doing.
• They make sure your computer is using the network efficiently
and securely, like adjusting the speed of your internet or
protecting your computer from online threats.

12 & 13. Backup, Recovery &
Virtualization
• Backup and Recovery:
• The operating system provides mechanisms for
backing up data and recovering it in case of
system failures, errors, or disasters.
• Virtualization:
• The operating system provides virtualization
capabilities that allow multiple operating
systems or applications to run on a single
physical machine.
• This can enable efficient use of resources and
flexibility in managing workloads.

14. Error-detecting Aids
• These contain methods that include the
• production of dumps,
• traces,
• error messages, and
• other debugging and error-detecting methods.
• The operating system constantly monitors the system to detect errors and avoid
malfunctioning computer systems.
• From time to time, the operating system checks the system for any external threat or malicious
software activity.
• It also checks the hardware for any type of damage.
• This process displays several alerts to the user so that the appropriate action can be taken
against any damage caused to the system.

15. Time-Sharing
• Time-Sharing:
• The operating system enables multiple
users to share a computer system and
its resources simultaneously by
providing time-sharing mechanisms
that allocate resources fairly and
efficiently.

16. System Calls
• The operating system provides a set of
system calls that enable applications
to interact with the operating system
and access its resources.
• System calls provide a standardized
interface between applications and the
operating system, enabling portability
and compatibility across different
hardware and software platforms.

What is Kernel?
• A kernel is the core part of an operating system.
• It acts as a bridge between software applications
and the hardware of a computer.
• The kernel manages system resources, such as
• the CPU, memory, and devices, ensuring everything works
together smoothly and efficiently.
• It handles tasks like running programs, accessing
files, and connecting to devices like printers and
keyboards.

Introduction of System Call
• A system call is a programmatic way in which a computer program requests a service from
the kernel of the operating system it is executed on / interact with the operating system.
• A computer program makes a system call when it requests the operating system’s kernel.
• System call provides the services of the operating system to the user programs via the
Application Program Interface(API).
• To allow a website or mobile app to retrieve data from a database or external service, such as social
media platforms, cloud storage or payment gateways.
• It provides an interface between a process and an operating system to allow user-level
processes to request services of the operating system.
• System calls are the only entry points into the kernel system. All programs needing resources
must use system calls.

Before an understanding of the working of system
calls in OS let us understand the important
concept of modes of operation.
In our computer system, we have two modes
available.
1. User Mode: In this mode, execution is done on
behalf of the user.
2. Monitor/Kernel-Mode: In this mode,
execution is done on behalf of OS.

What is a System Call?
• A system call is a mechanism used by programs to request services from the operating
system (OS).
• In simpler terms, it is a way for a program to interact with the underlying system, such as
accessing hardware resources or performing privileged operations.
• A user program can interact with the operating system using a system call.
• A number of services are requested by the program, and the OS responds by launching a
number of systems calls to fulfill the request.
• A system call can be written in high-level languages like C or Pascal or in assembly
language.
• If a high-level language is used, the operating system may directly invoke system calls,
which are predefined functions.

What is a System Call?
A system call is initiated by the program executing a specific
instruction, which triggers a switch to kernel mode, allowing
the program to request a service from the OS.
The OS then handles the request, performs the necessary
operations, and returns the result back to the program.
System calls are essential for the proper functioning of an
operating system, as they provide a standardized way for
programs to access system resources.
Without system calls, each program would need to
implement its methods for accessing hardware and system
services, leading to inconsistent and error-prone behavior.

Services Provided by System Calls
• Process Control:
• It handles the system calls for process creation, deletion, etc. Examples of
process control system calls are: Load, Execute, Abort, and Wait for Signal events
for process.
• File Management:
• File manipulation events like Creating, Deleting, Reading Writing etc are being
classified under file management system calls.
• Device Management:
• Device Management system calls are being used to request the device, release the
device, and logically attach and detach the device.
• Information Maintenance
• This type of system call is used to maintain the information about the system like
time and date.
• Communication:
• In order to have inter-process communications like send or receive the message,
create or delete the communication connections, to transfer status information
etc. communication system calls are used.

Features of System Calls
• Interface: System calls provide a well-defined interface between user programs and the operating system.
Programs make requests by calling specific functions, and the operating system responds by executing
the requested service and returning a result.
• Protection: System calls are used to access privileged operations that are not available to normal user
programs. The operating system uses this privilege to protect the system from malicious or unauthorized
access.
• Kernel Mode: When a system call is made, the program is temporarily switched from user mode to kernel
mode. In kernel mode, the program has access to all system resources, including hardware, memory,
and other processes.
• Context Switching: A system call requires a context switch, which involves saving the state of the
current process and switching to the kernel mode to execute the requested service. This can introduce
overhead, which can impact system performance.
• Error Handling: System calls can return error codes to indicate problems with the requested service.
Programs must check for these errors and handle them appropriately.
• Synchronization: System calls can be used to synchronize access to shared resources, such as files or
network connections. The operating system provides synchronization mechanisms, such as locks or
semaphores, to ensure that multiple programs can access these resources safely.

How does System Call Work?
• Here is a detailed explanation step by step how system calls work:
• Users need special resources: Sometimes programs need to do some special things that can’t be done without
the permission of the OS like reading from a file, writing to a file, getting any information from the hardware, or
requesting a space in memory.
• The program makes a system call request: There are special predefined instructions to make a request to the
operating system. These instructions are nothing but just a “system call”. The program uses these system calls
in its code when needed.
• Operating system sees the system call: When the OS sees the system call then it recognizes that the program
needs help at this time so it temporarily stops the program execution and gives all the control to a special part of
itself called ‘Kernel’. Now ‘Kernel’ solves the need of the program.
• The operating system performs the operations: Now the operating system performs the operation that is
requested by the program. Example: reading content from a file etc.
• Operating system give control back to the program : After performing the special operation, OS give control
back to the program for further execution of program .

Examples of a
System Call in
Windows and Unix
• System calls for Windows
and Unix come in many
different forms. These are
listed in the table below as
follows:
Process Windows Unix
Process Control
CreateProcess()
ExitProcess()
WaitForSingleObject()
Fork()
Exit()
Wait()
File manipulation
CreateFile()
ReadFile()
WriteFile()
Open()
Read()
Write()
Close()
Device
Management
SetConsoleMode()
ReadConsole()
WriteConsole()
Ioctl()
Read()
Write()
Information
Maintenance
GetCurrentProcessID()
SetTimer()
Sleep()
Getpid()
Alarm()
Sleep()
Communication
CreatePipe()
CreateFileMapping()
MapViewOfFile()
Pipe()
Shmget()
Mmap()
Protection
SetFileSecurity()
InitializeSecurityDescriptor()
SetSecurityDescriptorgroup()
Chmod()
Umask()
Chown()

Open():
• Accessing a file on a file system is possible with the open() system call.
• It gives the file resources it needs and a handle the process can use.
• A file can be opened by multiple processes simultaneously or just one process.
• Everything is based on the structure and file system.
Read():
• Data from a file on the file system is retrieved using it. In general, it accepts
three arguments:
• A description of a file.
• A buffer for read data storage.
• How many bytes should be read from the file
• Before reading, the file to be read could be identified by its file descriptor and opened
using the open() function.

Wait():
• In some systems, a process might need to hold off until another process has finished
running before continuing.
• When a parent process creates a child process, the execution of the parent process is
halted until the child process is complete.
• The parent process is stopped using the wait() system call. The parent process regains
control once the child process has finished running.
Write():
• Data from a user buffer is written using it to a device like a file. A program can produce
data in one way by using this system call. generally, there are three arguments:
• A description of a file.
• A reference to the buffer where data is stored.
• The amount of data that will be written from the buffer in bytes.

Fork():
• The fork() system call is used by processes to create copies of themselves.
• It is one of the methods used the most frequently in operating systems to
create processes.
• When a parent process creates a child process, the parent process’s execution
is suspended until the child process is finished.
• The parent process regains control once the child process has finished
running.
Exit():
• A system call called exit() is used to terminate a program.
• In environments with multiple threads, this call indicates that the thread
execution is finished.
• After using the exit() system function, the operating system recovers the
resources used by the process.

Disadvantages of System Call
• Performance Overhead: System calls involve switching between user mode and
kernel mode, which can slow down program execution.
• Security Risks: Improper use or vulnerabilities in system calls can lead to security
breaches or unauthorized access to system resources.
• Error Handling Complexity: Handling errors in system calls, such as resource
allocation failures or timeouts, can be complex and require careful programming.
• Compatibility Challenges: System calls may vary between different
operating systems, requiring developers to write code that works across multiple
platforms.
• Resource Consumption: System calls can consume significant system resources,
especially in environments with many concurrent processes making frequent calls.

Conclusion
• In conclusion, system calls are a important part of how
computer programs interact with the operating system.
• They provide a way for applications to request services from the OS,
such as accessing files, managing memory, or communicating over
networks.
• System calls act as a bridge between user-level programs and the
low-level operations handled by the operating system kernel.
• Understanding system calls is essential for developers to create
efficient and functional software that can leverage the full capabilities
of the underlying operating system.

Different types of operating systems
• While there exist many similarities between operating systems – such as critical shell and
kernel components – there is also plenty of variety.
• Where some OS utilize a graphical user interface (GUI), others will have a text-based,
command-line interface (CLI).
• The Operating System types encompass various variants, each tailored to distinct needs.
• Different operating systems serve different purposes and have different applications. Some OS
are suited for everyday tasks and functions, such as using a smartphone or personal laptop,
whereas others are required for more specialized work or tasks, such as gaming.
• All operating systems have one common goal - to manage and organize the resources and
processes of a computer. These resource managers include processes, threads, files, devices,
and networks.
• Operating systems evolved in response to technological advances and changed over time as
new hardware was developed.

Different types of operating systems
The main types of operating system are:
● Simple batch operating system
● Multi-programming batch operating system
● Multi-tasking operating system
● Multi-User Operating Syetem
● Multi-processing operating system
● Time-sharing operating system
● Distributed operating system
● Network operating system
● Real-time operating system
● Mobile operating system.

1. Batch Operating System
In batch operating system,
• Firstly, user prepares his job using punch cards.
• Then, he submits the job to the computer operator.
• Operator collects the jobs from different users and sort the jobs into batches with similar needs.
• Then, operator submits the batches to the processor one by one.
• All the jobs of one batch are executed together.
• This type of operating system does not interact with the computer directly.
• There is an operator which takes similar jobs having the same requirements and groups them into batches.
• It is the responsibility of the operator to sort jobs with similar needs.
• Batch Operating System is designed to manage and execute a large number of jobs efficiently by processing them in groups.

Advantages of Batch Operating System
● It saves the time that was being wasted earlier for each individual process in context switching from one environment to another
environment.
● No manual intervention is needed.
Disadvantages of Batch Operating System
● All the jobs of a batch are executed sequentially one after the other.
● The output is obtained only after all the jobs are executed.
● Thus, priority can not be implemented if a certain job has to be executed on an urgent basis.
● The jobs of a particular batch might take long time for their execution.
● This might lead to starvation to other jobs in other batches.
● If the jobs of a batch require some I/O operation, then CPU must wait till the I/O operation gets completed.
● Since I/O devices are very slow, CPU remains idle for a long time.
● CPU can not take any other job and execute it.
● Once a batch is submitted for execution, the user is not able to interact with any of his jobs.
● If a job requires the user to input data during run time, then user must wait till the other jobs of the batch get executed.
● This also increases the overall execution time.
Examples of Batch Operating Systems: Payroll Systems, Bank Statements, etc.

2. Multi-programming Batch operating system
• On a single processor computer, a multiprogramming OS can run many programs.
• In a multiprogramming OS, if one program must wait for an input/output transfer, the
other programmes are ready to use the CPU.
• As a result, different jobs may have to split CPU time. However, their jobs are not
scheduled to be completed at the same time.
• When software is run, it is referred to as a “Task,” “Process,” or “Job.”
• When compared to serial or batch processing systems, concurrent program executions
reduce system resource usage and increase throughput.
• Multiprogramming’s main purpose is to manage all of the system’s resources.
• The file system, transient area, command processor, and I/O control system are the main
components of a multiprogramming system.
• As a result, the multiprogramming OS is built to store many programs based on sub-
segmenting the transient area.
• The operating system’s essential functions are tied to the resource management processes.

Multiprogramming operating systems are divided into
two categories, and they are:
• Multitasking Operating System
• A multitasking OS allows two or more programmes to run
simultaneously.
• This is accomplished by the operating system transferring each
program into or out of memory one by one.
• When a program is switched out of the memory, it is saved on the disc
temporarily until it is needed again.
• Multiuser Operating System
• A multiuser operating system allows multiple users from various
terminals to share the processing time on a certain powerful central
machine.
• The operating system achieves this by frequently switching between
terminals, each of which is allotted a certain amount of processor time
on a central computer.
• Because the operating system on each terminal changes so frequently,
each user appears to have constant access to the central computer.
• When a system has a large number of users, the time it takes for the
central computer to respond becomes more apparent.

Advantages of Multiprogramming Operating System
• It has a faster response time.
• It may be beneficial to run multiple jobs in a single application at the same
time.
• It aids in the computer’s overall optimization of job throughput.
• The multiprogramming system can be used by multiple people at the same
time.
• In comparison to long-term work, short-term jobs are completed swiftly.
• It may aid in reducing turnaround time for short-duration tasks.
• It contributes to higher CPU utilisation and is never idle.
• The resources are wisely allocated.
Disadvantages of Multiprogramming Operating System
• It’s quite complex and sophisticated.
• CPU scheduling is necessary.
• Since all types of tasks get stored in the main memory, memory
management is required in the operating system.
• The more difficult challenge is managing all procedures and tasks.
• Long-term jobs will demand a long wait if it has a high number of jobs.

Examples of Multiprogramming Operating Systems
• Desktop operating systems, including Windows, macOS, and various Linux
distributions.
• These are contemporary operating systems that make use of a variety of
multiprogramming concepts.
• A system running one of these (or more) operating systems allows a user to run
multiple jobs at once. For instance, many games have been developed to utilize
just one processor core.
• One can send and receive text messages while simultaneously listening to
music on a phone running Android, iOS, or another mobile operating system.
• Application software, including media players, Office, and well-known web
browsers.
• Any modern web browser would allow a user to open as many windows or tabs
as necessary in order to visit multiple websites at once.

3. Multi-Processing Operating System
• Multiprocessing helps in performing parallel computing. There are several
processors in a system, and each of them can run multiple processes
simultaneously. The system’s throughput will be significantly increased.
• Multiprocessor operating systems are used in operating systems to boost the
performance of multiple CPUs within a single computer system.
• Multiple CPUs are linked together so that a job can be divided and executed more
quickly.
• When a job is completed, the results from all CPUs are compiled to provide the
final output. Jobs were required to share main memory, and they may often
share other system resources.
• Multiple CPUs can be used to run multiple tasks at the same time, for example,
UNIX.
• One of the most extensively used operating systems is the multiprocessing
operating system.
• The following diagram depicts the basic organisation of a typical multiprocessing
system.

Advantages of Multiprocessing OS
• Increased reliability: Processing tasks can be spread among numerous processors in the
multiprocessing system. This promotes reliability because if one processor fails, the task can
be passed on to another.
• Increased throughout: More work could be done in less time as the number of processors
increases.
• The economy of scale: Multiprocessor systems are less expensive than single-processor
computers because they share peripherals, additional storage devices, and power sources.
Disadvantages of Multiprocessing OS
• Multiprocessing operating systems are more complex and advanced since they manage many
CPUs at the same time.

Symmetrical
• Each processor in a symmetrical multiprocessing system runs the same copy of the OS, makes its own decisions, and
collaborates with other processes to keep the system running smoothly. CPU scheduling policies are straightforward. Any
new job that is submitted by a user could be assigned to the least burdened processor. It also means that at any given
time, all processors are equally taxed.
• Since the processors share memory along with the I/O bus or data channel, the symmetric multiprocessing OS is
sometimes known as a “shared everything” system. The number of processors in this system is normally limited to 16.
Characteristics
• Any processor in this system can run any process or job.
• Any CPU can start an Input and Output operation in this way.
Pros
• These are fault-tolerant systems. A few processors failing does not bring the whole system to a standstill.
Cons
• It is quite difficult to rationally balance the workload among processors.
• For handling many processors, specialised synchronisation algorithms are required.

Asymmetrical
• The processors in an asymmetric system have a master-slave relationship. In addition, one processor may serve as a master
or supervisor processor, while the rest are treated as illustrated below.
Characteristics
• In the asymmetric processing system represented above, CPU n1 serves as a supervisor, controlling the subsequent CPUs.
• Each processor in such a system is assigned a specific task, and the actions of the other processors are overseen by a master
processor.
Pros
• Because several processors are available for a single job, the execution of an I/O operation or application software in this
type of system may be faster in some instances.
Cons
• The processors are burdened unequally in this form of multiprocessing operating system. One CPU may have a large job
queue while another is idle.
• If a process handling a specific task fails in this system, the entire system will fail.

4. Time-Sharing Operating Systems
• Time-sharing enables many people, located at various terminals, to use a particular computer system at the same
time.
• Multitasking or Time-Sharing Systems is a logical extension of multiprogramming.
• Processor’s time is shared among multiple users simultaneously is termed as time-sharing.
• The main difference between Time-Sharing Systems and Multiprogrammed Batch Systems is that in case of
Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the
objective is to minimize response time.
• Multiple jobs are implemented by the CPU by switching between them, but the switches occur so frequently. So, the
user can receive an immediate response.
• For an example, in a transaction processing, the processor executes each user program in a short burst or quantum
of computation, i.e.; if n users are present, then each user can get a time quantum.
• Whenever the user submits the command, the response time is in few seconds at most.
• An operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time.
Computer systems which were designed primarily as batch systems have been modified to time-sharing systems.

Advantages of Timesharing operating systems are −
• It provides the advantage of quick response.
• This type of operating system avoids duplication of software.
• It reduces CPU idle time.
Disadvantages of Time-sharing operating systems are −
• Time sharing has problem of reliability.
• Question of security and integrity of user programs and data can be raised.
• Problem of data communication occurs.

5. Distributed Operating System
• These types of operating system is a recent advancement in the world of computer
technology and are being widely accepted all over the world and, that too, at a great pace.
• Various autonomous interconnected computers communicate with each other using a
shared communication network.
• Independent systems possess their own memory unit and CPU. These are referred to as
loosely coupled systems or distributed systems. These systems’ processors differ in size and
function.
• The Distributed Operating system is not installed on a single machine, it is divided into
parts, and these parts are loaded on different machines. A part of the distributed Operating
system is installed on each machine to make their communication possible.
• Distributed Operating systems are much more complex, large, and sophisticated than
Network operating systems because they also have to take care of varying networking
protocols.
• The major benefit of working with these types of the operating system is that it is always
possible that one user can access the files or software which are not actually present on his
system but some other system connected within this network i.e., remote access is enabled
within the devices connected in that network.

Advantages of Distributed Operating System
● Failure of one will not affect the other network communication, as all systems are independent of each other.
● Electronic mail increases the data exchange speed.
● Since resources are being shared, computation is highly fast and durable.
● Load on host computer reduces.
● These systems are easily scalable as many systems can be easily added to the network.
● Delay in data processing reduces.
Disadvantages of Distributed Operating System
● Failure of the main network will stop the entire communication.
● To establish distributed systems the language is used not well-defined yet.
● These types of systems are not readily available as they are very expensive. Not only that the underlying software is highly
complex and not understood well yet.

Examples of Distributed Operating Systems are LOCUS, etc.
Issues With Distributed Operating Systems
● Networking causes delays in the transfer of data between
nodes of a distributed system. Such delays may lead to an
inconsistent view of data located in different nodes, and
make it difficult to know the chronological order in which
events occurred in the system.
● Control functions like scheduling, resource allocation, and
deadlock detection have to be performed in several nodes to
achieve computation speedup and provide reliable operation
when computers or networking components fail.
● Messages exchanged by processes present in different nodes
may travel over public networks and pass through computer
systems that are not controlled by the distributed operating
system. An intruder may exploit this feature to tamper with
messages, or create fake messages to fool the authentication
procedure and masquerade as a user of the system.

6. 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 types of operating systems allow shared access to files, printers, security,
applications, and other networking functions over a small private network.
• One more important aspect of Network Operating Systems is that all the users
are well aware of the underlying configuration, of all other users within the
network, their individual connections, etc. and that’s why these computers are
popularly known as tightly coupled systems.
• The OS specializes in network devices such as a router, switch, or firewall. The
OS manages these network resources. The OS supports workstations, Personal
Computers (PCs), older terminals connected on a Local Area Network (LAN).
• Examples of Network OSs are Microsoft Windows Server 2003, Microsoft
Windows Server 2008, UNIX, Linux, Mac OS X, etc.
• The OS thus facilitates connecting and communicating various autonomous
computers over a network. Its purpose is to support workstations, share
databases, sharing of application, and sharing of file and printer access
amongst computers in a network.

Advantages of Network Operating System
● Highly stable centralized servers.
● Security concerns are handled through servers.
● New technologies and hardware up-gradation are easily
integrated into the system.
● Server access is possible remotely from different locations
and types of systems.
Disadvantages of Network Operating System
● Servers are costly.
● User has to depend on a central location for most operations.
● Maintenance and updates are required regularly.

7. Real-Time Operating System
• These types of OSs serve real-time systems. The time interval required to process and respond to inputs is very small. This time interval is called response
time. Real-time systems are used when there are time requirements that are very strict like missile systems, air traffic control systems, robots, etc.
• All real time operating systems are designed to execute their task within a particular time interval, and thus they have to be fast enough to be up to their
deadline.
• Time constraints related with real-time systems simply means that time interval allotted for the response of the ongoing program. This deadline means
that the task should be completed within this time interval. Hence, they are used in air traffic control systems.
• Correctness of result is also a crucial feature of real time systems and they not only need to produce correct result but that too needs to be
produced in the given time limit and deadline else even if correct result is delivered but after deadline it’s considered a failure of the OS.
• Real-time systems are concurrent that means it can respond to a several number of processes at a time. There are several different tasks going on within
the system and it responds accordingly to every task in short intervals. This makes the real-time systems concurrent systems.
• Even if the load is heavy on a system like it has to respond to multiple processes then also it must meet every deadline. It still responds to every query
within time this provides stability to the Real time OS.
• There are several different tasks going on within the system and it responds accordingly to every task in short intervals. This makes the real-time systems
concurrent systems.
Types of Real-Time Operating Systems
● Hard Real-Time Systems: Hard Real-Time OSs are meant for applications where time constraints are very strict and even the shortest possible
delay is not acceptable. These systems are built for saving life like automatic parachutes or airbags which are required to be readily available in
case of an accident. Virtual memory is rarely found in these systems.
● Soft Real-Time Systems: These OSs are for applications where time-constraint is less strict.

• The Application of a Real-Time system exists in the case
of military applications, if you want to drop a missile,
then the missile is supposed to be dropped with a
certain precision.

Advantages of RTOS
● Maximum Consumption: Maximum utilization of devices and systems, thus more output from all the
resources.
● Task Shifting: The time assigned for shifting tasks in these systems is very less. For example, in older
systems, it takes about 10 microseconds in shifting from one task to another, and in the latest systems,
it takes 3 microseconds.
● Focus on Application: Focus on running applications and less importance on applications that are in
the queue.
● Real-time operating system in the embedded system: Since the size of programs is small, RTOS can
also be used in embedded systems like in transport and others.
● Error Free: These types of systems are error-free.
● Memory Allocation: Memory allocation is best managed in these types of systems.

Disadvantages of RTOS
● Limited Tasks: Very few tasks run at the same time and their concentration is very less on a few applications
to avoid errors.
● Use heavy system resources: Sometimes the system resources are not so good and they are expensive as
well.
● Complex Algorithms: The algorithms are very complex and difficult for the designer to write on.
● Device driver and interrupt signals: It needs specific device drivers and interrupts signal to respond
earliest to interrupts.
● Thread Priority: It is not good to set thread priority as these systems are very less prone to switching tasks.
Examples of Real-Time Operating Systems are Scientific experiments, medical imaging systems, industrial
control systems, weapon systems, robots, air traffic control systems, etc.

Conclusion
Operating systems come in various types, each used for specific needs. Whether
it’s managing large batches of jobs, enabling multiple users to work
simultaneously, coordinating networked computers, or ensuring timely execution
in critical systems. Understanding these types helps in choosing the right
operating system for the right job, ensuring efficiency and effectiveness.

Operating Systems unit 1 & 2 - BBA / MBA

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