This document provides an overview of operating systems, including their objectives, components, functions, and structures. It describes what an operating system is and its main goals of executing programs, making the computer convenient to use, and using hardware efficiently. The major components covered include process management, memory management, file management, and more. Different types of operating systems are explored such as batch, time-sharing, distributed, real-time, and network operating systems. Operating system structures like monolithic and layered architectures are also summarized.

1. OPERATING SYSTEMS

2. Objectives
• To describe the basic organization of computer systems
• To provide a grand tour of the major components of operating
systems
• To give an overview of the many types of computing environments
• To explore several open-source operating systems

3. What is an Operating
System?
⦿ A program that acts as an intermediary
between a user of a computer and the
computer hardware
⦿ Operating system goals:
› Execute user programs and make solving
user problems easier
› Make the computer system convenient to
use
› Use the computer hardware in an efficient
manner

4. ⦿ A collection of programs which control
the resources of a computer system.
⦿ Written in low-level language(machine
dependent)
⦿ An interface between users and
hardware
⦿ When the computer is on ,OS will first load
into the main memory

5. Computer System Structure
⦿ Computer system can be divided into four
components:
› 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. Four Components of a
Computer System

7. What Operating Systems Do

8. ⦿ Process Management
⦿ The process management activities
handled by the OS are—
1. control access to shared resources like
file, memory, I/O and CPU
2. control execution of applications
3. create, execute and delete a process
(system process or user process)
4. cancel or resume a process
5. schedule a process
6. synchronization, communication and
deadlock handling for processes.

9. ⦿ Memory Management
⦿ The activities of memory management handled by
OS are—
1. allocate memory
2. free memory
3. re-allocate memory to a program when a used
block is freed
4. keep track of memory usage
⦿ File Management
⦿ The file management tasks include —
1. create and delete both files and directories
2. provide access to files
3. allocate space for files
4. keep back-up of files
5. secure files

10. ⦿ Device Management
⦿ The device management tasks handled by OS are—
1. open, close and write device drivers
2. communicate, control and monitor the device
driver
⦿ Protection and Security
⦿ OS protects the resources of system. User
authentication, file attributes like read, write,
encryption, and back-up of data are used by OS to
provide basic protection.
⦿ User Interface or Command Interpreter
⦿ Operating system provides an interface between the
computer user and the computer hardware. The user
interface is a set of commands or a graphical user
interface via which the user interacts with the
applications and the hardware.

11. Types of operating system
⦿ 1. Batch Operating System –
This type of operating system does not
interact with the computer directly.
There is an operator which takes similar
jobs having same requirement and
group them into batches. It is the
responsibility of operator to sort the jobs
with similar needs.

13. Advantages of Batch Operating System:
It is very difficult to know the time required by any job
to complete.
Processors of the batch systems know how long the job
would be when it is in queue.
⦿ Multiple users can share the batch systems
⦿ The idle time for batch system is very less
⦿ It is easy to manage large work repeatedly in batch
systems
Disadvantages of Batch Operating System:
⦿ The computer operators should be well known with
batch systems
⦿ Batch systems are hard to debug
⦿ It is sometime costly
⦿ The other jobs will have to wait for an unknown time if
any job fails
Examples of Batch based Operating System:
⦿ Payroll System, Bank Statements etc.

14. 2. 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 time that each task gets to execute
is called quantum. After this time interval
is over OS switches over to next task.

15. Advantages of Time-Sharing OS:
⦿ Each task gets an equal opportunity
⦿ CPU idle time can be reduced
Disadvantages of Time-Sharing OS:
⦿ Reliability problem
⦿ One must have to take care of security
and integrity of user programs and data
⦿ Data communication problem
Examples of Time-Sharing OSs are:
Multics, Unix etc.

16. ⦿ 3. Distributed Operating System –
. Various autonomous interconnected
computers communicate each other
using a shared communication network.
Independent systems possess their own
memory unit and CPU.
⦿ These are referred as loosely coupled
systems or distributed systems. These
system’s processors differ in size and
function.
⦿ The major benefit of working with these
types of operating system is that remote
access is enabled within the devices
connected in that network.

18. Advantages of Distributed Operating System:
⦿ Failure of one will not affect the other network
communication, as all systems are
independent from each other
⦿ 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
⦿ These types of systems are not readily available
as they are very expensive.
Examples of Distributed Operating System are-
LOCUS etc.

19. ⦿ 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.
⦿ 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.

20. Advantages of Network Operating System:
⦿ Highly stable centralized servers
⦿ Security concerns are handled through servers
⦿ New technologies and hardware up-gradation
are easily integrated to the system
⦿ Server access are possible remotely from
different locations and types of systems
Disadvantages of Network Operating System:
⦿ Servers are costly
⦿ User has to depend on central location for
most operations
⦿ Maintenance and updates are required
regularly
⦿ Examples of Network Operating System
are: Microsoft Windows Server 2003, Microsoft
Windows Server 2008, UNIX, Linux, .

21. Real-Time Operating System –
These types of OSs serves the real-time systems.
⦿ Real-time systems are used when there are time
requirements are very strict like missile systems, air
traffic control systems, robots etc.
⦿ Two types of Real-Time Operating System which are
as follows:
⦿ Hard Real-Time Systems:
These OSs are meant for the 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 air
bags which are required to be readily available in
case of any accident.
⦿ Soft Real-Time Systems:
These OSs are for applications where for time-
constraint is less strict.

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

23. Disadvantages of RTOS:
⦿ Limited Tasks: Very few tasks run at the
same time and their concentration is on
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.
⦿ Examples of Real-Time Operating
Systems are: Scientific experiments,
medical imaging systems, industrial
control systems, weapon systems, robots,
air traffic control systems, etc.

24. Operating System Structure
Common System Components:
1. Process Management
2. Main Memory Management
3. Secondary-Storage Management
4. I/O System Management
5. File Management
6. Protection System
7. Networking
8. Command-Interpreter System

25. Process Management
⦿ A process is a program in execution. A
process needs certain resources,
including CPU time, memory, files, and
I/O devices, to accomplish its task.
⦿ The operating system is responsible for
the following activities in connection with
process management.
› Process creation and deletion.
› process suspension and resumption.
› Provision of mechanisms for:
●process synchronization
●process communication

26. Main-Memory Management
⦿ Memory is a large array of words or bytes,
each with its own address. It is a repository of
quickly accessible data shared by the CPU
and I/O devices.
⦿ Main memory is a volatile storage device. It
loses its contents in the case of system failure.
⦿ The operating system is responsible for the
following activities in connections with memory
management:
› Keep track of which parts of memory are currently
being used and by whom.
› Decide which processes to load when memory
space becomes available.
› Allocate and reallocate memory space as needed.

27. Secondary-Storage Management
⦿ Since main memory (primary storage) is
volatile and too small to accommodate all
data and programs permanently, the
computer system must provide secondary
storage to back up main memory.
⦿ Most modern computer systems use disks as
the principle on-line storage medium, for
both programs and data.
⦿ The operating system is responsible for the
following activities in connection with disk
management:
› Free space management
› Storage allocation
› Disk scheduling

28. I/O System Management
⦿ The I/O system consists of:
› A buffer-caching system
› A general device-driver interface
› Drivers for specific hardware devices
Protection System
⦿ Protection refers to a mechanism for
controlling access by programs, processes,
or users to both system and user resources.
⦿ The protection mechanism must:
› distinguish between authorized and
unauthorized usage.
› specify the controls to be imposed.
› provide a means of enforcement

29. File Management
⦿ A file is a collection of related information
defined by its creator. Commonly, files
represent programs and data.
⦿ The operating system is responsible for the
following activities in connections with file
management:
› File creation and deletion.
› Directory creation and deletion.
› Support of primitives for manipulating files and
directories.
› Mapping files onto secondary storage.
› File backup on stable (nonvolatile) storage
media.

30. Networking (Distributed Systems)
⦿ A distributed system is a collection
processors that do not share memory or a
clock. Each processor has its own local
memory.
⦿ The processors in the system are connected
through a communication network.
⦿ A distributed system provides user access to
various system resources.
⦿ Access to a shared resource allows:
› Computation speed-up
› Increased data availability
› Enhanced reliability

31. Command-Interpreter System
⦿ Many commands are given to the
operating system by control statements
which deal with:
› process creation and management
› I/O handling
› secondary-storage management
› main-memory management
› file-system access
› protection
› networking

32. Operating System Services
⦿ Program execution – system capability to load a
program into memory and to run it.
⦿ I/O operations – since user programs cannot
execute I/O operations directly, the operating system
must provide some means to perform I/O.
⦿ File-system manipulation – program capability to
read, write, create, and delete files.
⦿ Communications – exchange of information
between processes executing either on the same
computer or on different systems tied together by a
network. Implemented via shared memory or
message passing.
⦿ Error detection – ensure correct computing by
detecting errors in the CPU and memory hardware, in
I/O devices, or in user programs.

33. Additional Operating System Functions
Additional functions exist not for helping
the user, but rather for ensuring efficient
system operations.
•Resource allocation – allocating resources to
multiple users or multiple jobs running at the
same time.
•Accounting – keep track of and record
which users use how much and what kinds of
computer resources for account billing or for
accumulating usage statistics.
•Protection – ensuring that all access to
system resources is controlled.

34. ⦿ There are two modes of operation in the
operating system to make sure it works
correctly. These are user mode and
kernel mode.

35. ⦿ User Mode
⦿ The system is in user mode when the operating system is running a user
application such as handling a text editor.
⦿ The transition from user mode to kernel mode occurs when the application
requests the help of operating system or an interrupt or a system call
occurs.
⦿ The mode bit is set to 1 in the user mode. It is changed from 1 to 0 when
switching from user mode to kernel mode.
⦿ Kernel Mode
⦿ The system starts in kernel mode when it boots and after the operating
system is loaded, it executes applications in user mode.
⦿ There are some privileged instructions that can only be executed in kernel
mode.
⦿ These are interrupt instructions, input output management etc.
⦿ If the privileged instructions are executed in user mode, it is illegal and a
trap is generated.
⦿ The mode bit is set to 0 in the kernel mode. It is changed from 0 to 1 when
switching from kernel mode to user mode.

37. kernel
Kernel Mode
⦿ When CPU is in kernel mode, the code being executed
can access any memory address and any hardware
resource.
⦿ Hence kernel mode is a very privileged and powerful
mode.
⦿ If a program crashes in kernel mode, the entire system will
be halted.
User Mode
⦿ When CPU is in user mode, the programs don't have direct
access to memory and hardware resources.
⦿ In user mode, if any program crashes, only that particular
program is halted.
⦿ That means the system will be in a safe state even if a
program in user mode crashes.
⦿ Hence, most programs in an OS run in user mode.
⦿

38. System Calls
⦿ System calls provide the interface between a
running program and the operating system.
› Generally available as assembly-language
instructions.
⦿ Three general methods are used to pass
parameters between a running program and
the operating system.
› Pass parameters in registers.
› Store the parameters in a table in memory,
and the table address is passed as a
parameter in a register.
› Push (store) the parameters onto the stack
by the program, and pop off the stack by
operating system.

39. System call
⦿ A System Call is the main way a user
program interacts with the Operating
System

40. HOW A SYSTEM CALL WORKS
∙ Obtain access to system space
∙ Do parameter validation
∙ System resource collection ( locks on
structures )
∙ Ask device/system for requested item
∙ Suspend waiting for device
∙ Interrupt makes this thread ready to run
∙ Wrap-up
∙ Return to user

41. There are 11 (or more) steps in making the system call
read (fd, buffer, nbytes)
read(fd, buffer, nbytes) Read data from a file into a buffer

42. These are examples of various system calls.

43. operating system structure:
⦿ An operating system might have many
structure
⦿ 1. Monolithic architecture of operating
system

44. ⦿ It is the oldest architecture used for developing
operating system.
⦿ Operating system resides on kernel for anyone to
execute.
⦿ System call is involved i.e. Switching from user
mode to kernel mode and transfer control to
operating system shown as event 1.
⦿ operating system then examines the parameter of the
call to determine which system call is to be carried
out shown in event 2.
⦿ Next, the operating system index’s into a table that
contains procedure that carries out system call. This
operation is shown in events3.
⦿ Finally, it is called when the work has been
completed and the system call is finished, control is
given back to the user mode as shown in event 4.

45. 2. Layered Architecture of operating system
⦿ the operating system is broken up into number of
layers.
⦿ The bottom layer (layer 0) is the hardware layer and
the highest layer (layer n) is the user interface layer
as shown in the figure.

46. Virtual machine
❖ Virtual machine is an illusion of a real machine.
❖ It is created by a real machine operating system, which
make a single real machine appears to be several real
machine.
❖ Actually, virtual machine can run several operating
systems at once, each of them on its virtual machine.
The concepts of virtual machine are:-
a. Control program (cp):- cp creates the environment in
which virtual machine can execute. It gives to each user
facilities of real machine such as processor, storage I/0
devices.
B. conversation monitor system (cons):- cons is a system
application having features of developing program. It
contains editor, language translator, and various
application packages.
c. Remote spooling communication system (RSCS):-
provide virtual machine with the ability to transmit and
receive file in distributed system.
d. IPCS (interactive problem control system):- it is used to
fix the virtual machine software problems.