An operating system is an interface between a computer user and the computer hardware. It performs basic tasks like file management, memory management, process management, input/output handling, and controlling peripheral devices. Popular operating systems include Linux, Windows, and OS X. The document then discusses the components of a computer system and provides examples of computer hardware components like the processor, memory, disks, I/O devices, and bus. It also covers operating system concepts like processes, address spaces, files, input/output, and protection.

1. INTRODUCTION TO
OPERATING SYSTEMS
UNIT I
Prof. Arti Gavas

2. What is an Operating System?
 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,
Windows, OS X, VMS, OS/400, AIX, z/OS, etc.
4/27/2020
Prof. Arti
2

3. Your Mom
4/27/2020 Prof. Arti Gavas 3
Operating System Acts as a mother of a computer System.

4. Four Components of a Computer
System
4/27/2020 Prof. Arti Gavas 4

5. An Operating System provides
services to both the users and to
the programs.
• It provides programs an environment to
execute.
• It provides users the services to execute the
programs in a convenient manner.
4/27/2020 Prof. Arti Gavas 5

6. Following are a few common services
provided by an operating system
• Program execution
• I/O operations
• File System manipulation
• Communication
• Error Detection
• Resource Allocation
• Protection
4/27/2020 Prof. Arti Gavas 6
https://www.tutorialspoint.com/operating_system/os_services.htm
Read More

7. History of Operating Systems
• The First Generation (1945–55) Vacuum
Tubes and Plug-boards
• The Second Generation (1955–65)
Transistors and Batch Systems
• The Third Generation (1965–1980) ICs and
Multiprogramming
• The Fourth Generation (1980–Present)
Personal Computers
• The next Generation: Mobile Computers
4/27/2020 Prof. Arti Gavas 7

8. History of Operating Systems
4/27/2020 Prof. Arti Gavas 8

9. Computer Hardware
4/27/2020 Prof. Arti Gavas 9
What is the relationship
between operating
systems and computer
hardware?
Operating system helps to
make computer hardware
available to the application
programs.
Without Operating System
we cannot access computer
hardware.

10. Computer Hardware
• Hardware is directed by the software(OS) to execute any
command or instruction. A combination of hardware and
software forms a usable computing system.
4/27/2020 Prof. Arti Gavas 10

11. Computer Hardware: Processor
• The term processor is used interchangeably with
the term central processing unit (CPU).
• The processor in a personal computer or embedded
in small devices is often called a microprocessor.
That term simply means that the processor's
elements are contained on a single integrated
circuitry (IC) chip.
• Most processors today are multi-core, which means
that the IC contains two or more processors for
enhanced performance, reduced power
consumption and more efficient simultaneous
processing of multiple tasks.
4/27/2020 Prof. Arti Gavas 11

12. Computer Hardware: Memory
• A memory is just like a human brain.
• It is used to store data and instructions.
• Computer memory is the storage space in the computer,
where data is to be processed and instructions required
for processing are stored.
• Memory is primarily of three types −
 Cache Memory
 Primary Memory/Main Memory
 Secondary Memory
4/27/2020 Prof. Arti Gavas 12

13. Computer Hardware: Memory
• A memory is just like a human brain.
• It is used to store data and instructions.
• Computer memory is the storage space in the computer,
where data is to be processed and instructions required
for processing are stored.
• Memory is primarily of three types −
 Cache Memory
 Primary Memory/Main Memory
 Secondary Memory
4/27/2020 Prof. Arti Gavas 13

14. Types of Memory
4/27/2020 Prof. Arti Gavas 14

15. Types of Memory
4/27/2020 Prof. Arti Gavas 15
Cache Memory
 Cache memory is a very high speed semiconductor
memory which can speed up the CPU.
 It acts as a buffer between the CPU and the main
memory.
 It is used to hold those parts of data and program which
are most frequently used by the CPU.
 The parts of data and programs are transferred from the
disk to cache memory by the operating system, from
where the CPU can access them.
Advantages
Cache memory is faster than main memory.
It consumes less access time as compared to main memory.
It stores the program that can be executed within a short
period of time.
It stores data for temporary use.
Disadvantages
Cache memory has limited capacity.
It is very expensive.

16. Types of Memory
4/27/2020 Prof. Arti Gavas 16
Primary Memory (Main Memory)
 Primary memory holds only those data and instructions on
which the computer is currently working.
 It has a limited capacity and data is lost when power is
switched off.
 It is generally made up of semiconductor device.
 These memories are not as fast as registers.
Characteristics of Main Memory
 These are semiconductor memories.
 It is known as the main memory.
 Usually volatile memory.
 Data is lost in case power is switched off.
 It is the working memory of the computer.
 Faster than secondary memories.
 A computer cannot run without the primary memory.

17. Types of Memory
4/27/2020 Prof. Arti Gavas 17
Secondary Memory
 This type of memory is also known as external memory or
non-volatile.
 It is slower than the main memory.
 These are used for storing data/information permanently.
CPU directly does not access these memories, instead
they are accessed via input-output routines.
 The contents of secondary memories are first transferred
to the main memory, and then the CPU can access it. For
example, disk, CD-ROM, DVD, etc.
Characteristics of Secondary Memory
 These are magnetic and optical memories.
 It is known as the backup memory.
 It is a non-volatile memory.
 Data is permanently stored even if power is switched off.
 It is used for storage of data in a computer.
 Computer may run without the secondary memory.
 Slower than primary memories.

18. • Most basic hard drives consist of a number of disk platters that
are positioned around a spindle inside a sealed chamber.
• The chamber also includes read-and-write heads and motors.
• The motor is used to spin the platters, which hold the data, at
up to 15,000 rotations per minute (a higher rpm number results
in faster performance).
4/27/2020 Prof. Arti Gavas 18
Computer Hardware: Disk

19. • Input/output device. Alternatively referred to as an IO device,
an input/output device is any hardware used by a human
operator or other systems to communicate with a computer.
• As the name suggests, input/output devices are capable of
sending data (output) to a computer and receiving data from a
computer (input).
• Examples of input/output devices:
 CD-R/RW, DVD
 Digital camera
 Floppy diskette drive
 Hard drives
 Modem
 Network adapter
 SD Card
 Touch screen
 USB thumb drives
4/27/2020 Prof. Arti Gavas 19
Computer Hardware: I/O Devices

20. Computer Hardware: Bus
• When referring to a computer, the bus also known as the
address bus, data bus, or local bus is a data connection
between two or more devices connected to the computer.
• For example, a bus enables a computer processor to
communicate with the memory or a video card to communicate
with the memory.
• The bus contains multiple wires (signal lines) that contain
addressing information that describes the memory location of
where the data is being sent or where it is being retrieved.
• Each wire in the bus carries a single bit of information, which
means the more wires a bus has the more information it can
address.
• For example, a computer with a 32-bit address bus can address
4 GB of memory, and a computer with a 36-bit bus can address
64 GB of memory.
4/27/2020 Prof. Arti Gavas 20

21. Computer Hardware: Bus
4/27/2020 Prof. Arti Gavas 21

22. Computer Hardware: Booting Your Computer
• Booting is a startup sequence that starts the operating
system of a computer when it is turned on.
• A boot sequence is the initial set of operations that the
computer performs when it is switched on.
• Every computer has a boot sequence.
• The boot sequence is important to know for customizing and
troubleshooting your computer.
• Boot Loader
 The program that starts the “chain reaction” which ends with the
entire operating system being loaded is known as the boot loader
(or bootstrap loader).
• Boot Devices
 The boot device is the device from which the operating system
is loaded. A modern PC BIOS (Basic Input/Output System)
supports booting from various devices. These include the local hard
disk drive, optical drive(CD), floppy drive, a network interface card,
and a USB device.
4/27/2020 Prof. Arti Gavas 22

23. Types of Operating Systems
4/27/2020 Prof. Arti Gavas 23
Batch operating system
Time-sharing operating systems
Distributed operating System
Network operating System
Real Time operating System
• Hard real-time systems
• Soft real-time systems

24. Types of Operating Systems: Batch operating system
• The users of a batch operating system do not interact with the
computer directly.
• Each user prepares his job on an off-line device like punch
cards and submits it to the computer operator.
• To speed up processing, jobs with similar needs are batched
together and run as a group. The programmers leave their
programs with the operator and the operator then sorts the
programs with similar requirements into batches.
• The problems with Batch Systems are as follows −
 Lack of interaction between the user and the job.
 CPU is often idle, because the speed of the mechanical I/O devices
is slower than the CPU.
4/27/2020 Prof. Arti Gavas 24

25. Types of Operating Systems: Time-sharing operating systems
• Time-sharing is a technique which enables many people,
located at various terminals, to use a particular computer
system at the same time.
• Time-sharing or multitasking is a logical extension of
multiprogramming.
• Processor's time which is shared among multiple users
simultaneously is termed as time-sharing.
• Advantages of Timesharing operating systems are as follows −
 Provides the advantage of quick response.
 Reduces CPU idle time.
• Disadvantages of Time-sharing operating systems are as
follows −
 Question of security and integrity of user programs and data.
 Problem of data communication.
4/27/2020 Prof. Arti Gavas 25

26. Types of Operating Systems: Distributed operating System
• Distributed systems use multiple central processors to serve
multiple real-time applications and multiple users.
• Data processing jobs are distributed among the processors
accordingly.
• The processors communicate with one another through
various communication lines.
• Processors in a distributed system may vary in size and
function. These processors are referred as sites, nodes,
computers, and so on.
• The advantages of distributed systems are as follows −
 With resource sharing facility, a user at one site may be able to use
the resources available at another.
 Speedup the exchange of data with one another via electronic mail.
 If one site fails in a distributed system, the remaining sites can
potentially continue operating.
 Reduction of the load on the host computer.
 Reduction of delays in data processing.
4/27/2020 Prof. Arti Gavas 26

27. Types of Operating Systems: Network operating System
• A Network Operating System runs on a server and provides the server
the capability to manage data, users, groups, security, applications, and
other networking functions.
• The primary purpose of the network operating system is to allow
shared file and printer access among multiple computers in a
network, typically a local area network (LAN), a private network or to
other networks.
• The advantages of network operating systems are as follows −
 Centralized servers are highly stable.
 Security is server managed.
 Upgrades to new technologies and hardware can be easily integrated
into the system.
 Remote access to servers is possible from different locations and types
of systems.
• The disadvantages of network operating systems are as follows −
 High cost of buying and running a server.
 Dependency on a central location for most operations.
 Regular maintenance and updates are required.
4/27/2020 Prof. Arti Gavas 27

28. Types of Operating Systems: Real Time operating System
• A real-time system is defined as a data processing system in
which the time interval required to process and respond to
inputs is so small that it controls the environment.
• Real-time systems are used when there are rigid time
requirements on the operation of a processor or the flow of
data and real-time systems can be used as a control device in a
dedicated application.
• A real-time operating system must have well-defined, fixed
time constraints, otherwise the system will fail.
• For example, Scientific experiments, medical imaging systems,
industrial control systems, weapon systems, robots, air traffic
control systems, etc.
4/27/2020 Prof. Arti Gavas 28

29. Two Types of real-time operating systems
• Hard real-time systems
 Hard real-time systems guarantee that critical tasks
complete on time.
 In hard real-time systems, secondary storage is limited or
missing and the data is stored in ROM.
 In these systems, virtual memory is almost never found.
• Soft real-time systems
 Soft real-time systems are less restrictive.
 A critical real-time task gets priority over other tasks and
retains the priority until it completes.
 Soft real-time systems have limited utility than hard real-
time systems.
 For example, multimedia, virtual reality, Advanced Scientific
Projects like undersea exploration and planetary rovers, etc.
4/27/2020 Prof. Arti Gavas 29

30. Few more Types of Operating
Systems
Multi-user and Single-user Operating Systems
Multi-tasking and Single-tasking Operating Systems
Mainframe Operating Systems
Multiprocessor Operating Systems
Personal Computer Operating Systems
Handheld Computer Operating Systems
Mobile Operating System
Online and Offline Processing
Embedded Operating Systems
Sensor Node Operating Systems
Smart Card Operating Systems
4/27/2020 Prof. Arti Gavas 30

31. Operating System Concepts
Software Developers Need to Remember
Process
Address
Spaces
Files
Input/
Outputs
Protection
The Shell
4/27/2020 Prof. Arti Gavas 31

32. Process
• A process is a program in execution.
• Process is not as same as program code but a lot more than it.
• A process is an 'active' entity as opposed to program which is
considered to be a 'passive' entity. Attributes held by process
include hardware state, memory, CPU etc.
• Process memory is divided into four sections for efficient
working :
 The Text section is made up of the compiled program code, read
in from non-volatile storage when the program is launched.
 The Data section is made up the global and static variables,
allocated and initialized prior to executing the main.
 The Heap is used for the dynamic memory allocation, and is
managed via calls to new, delete, malloc, free, etc.
 The Stack is used for local variables. Space on the stack is
reserved for local variables when they are declared.
4/27/2020 Prof. Arti Gavas 32

33. Address Spaces
• The range of virtual addresses that the operating system
assigns to a user or separately running program is called an
address space.
• This is the area of contiguous virtual addresses available for
executing instructions and storing data.
• The range of virtual addresses in an address space starts at
zero and can extend to the highest address permitted by the
operating system architecture.
4/27/2020 Prof. Arti Gavas 33

34. Files
• A file is a named collection of related information that is
recorded on secondary storage such as magnetic disks,
magnetic tapes and optical disks.
• In general, a file is a sequence of bits, bytes, lines or records
whose meaning is defined by the files creator and user.
• File Structure
 A File Structure should be according to a required format that the
operating system can understand.
 A file has a certain defined structure according to its type.
 A text file is a sequence of characters organized into lines.
 A source file is a sequence of procedures and functions.
 An object file is a sequence of bytes organized into blocks that are
understandable by the machine.
 When operating system defines different file structures, it also
contains the code to support these file structure. Unix, MS-DOS
support minimum number of file structure.
4/27/2020 Prof. Arti Gavas 34

35. Files
• File Type
 File type refers to the ability of the operating system to distinguish
different types of file such as text files source files and binary files
etc.
 Many operating systems support many types of files.
 Operating system like MS-DOS and UNIX have the following types
of files −
 Ordinary files
• These are the files that contain user information.
• These may have text, databases or executable program.
• The user can apply various operations on such files like add, modify,
delete or even remove the entire file.
 Directory files
• These files contain list of file names and other information related to
these files.
 Special files
• These files are also known as device files.
• These files represent physical device like disks, terminals, printers,
networks, tape drive etc.
4/27/2020 Prof. Arti Gavas 35

36. Input/ Output
• Humans interact with machines by providing information
through IO devices.
• Also, much of whatever a computer system provides as on-line
services is essentially made available through specialized
devices such as screen displays, printers, keyboards, mouse,
etc.
• Clearly, management of all these devices can affect the
throughput of a system. For this reason, input output
management also becomes one of the primary responsibilities
of an operating system.
• Issues in IO Management
 The need for a human to input information and receive output from
a computer.
 The need for a device to input information and receive output from
a computer.
 The need for computers to communicate (receive/send information)
over networks.
4/27/2020 Prof. Arti Gavas 36

37. Protection
• As computer systems have become more sophisticated and
pervasive in their applications, the need to protect their integrity
has also grown.
• Protection refers to a mechanism for controlling the access of
programs, processes, or users to the resources defined by a
computer system.
• This mechanism must provide a means for specifying the
controls to be imposed, together with a means of enforcement.
4/27/2020 Prof. Arti Gavas 37

38. The Shell
• Your interface to the operating system is called a shell.
• The shell is the outermost layer of the operating system.
• Shells incorporate a programming language to control
processes and files, as well as to start and control other
programs.
• The shell manages the interaction between you and the
operating system by prompting you for input, interpreting that
input for the operating system, and then handling any resulting
output from the operating system.
• Shells provide a way for you to communicate with the operating
system.
• This communication is carried out either interactively (input from
the keyboard is acted upon immediately) or as a shell script.
• A shell script is a sequence of shell and operating system
commands that is stored in a file.
4/27/2020 Prof. Arti Gavas 38

39. The Kernel
• The kernel is the central module of an operating system (OS).
• It is the part of the operating system that loads first, and it
remains in main memory.
• Because it stays in memory, it is important for the kernel to be
as small as possible while still providing all the essential
services required by other parts of the operating system and
applications.
• The kernel code is usually loaded into a protected area of
memory to prevent it from being overwritten by programs or
other parts of the operating system.
4/27/2020 Prof. Arti Gavas 39

40. System Calls
• a system call is the programmatic way in which a computer
program requests a service from the kernel of the operating
system it is executed on.
• A system call is a way for programs to interact with the
operating system.
• A computer program makes a system call when it makes a
request to the operating system’s kernel.
• System call provides the services of the operating system to the
user programs via Application Program Interface(API).
• It provides an interface between a process and 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.
4/27/2020 Prof. Arti Gavas 40

41. Services Provided by System Calls
1. Process creation and management
2. Main memory management
3. File Access, Directory and File system management
4. Device handling(I/O)
5. Protection
6. Networking, etc.
• Types of System Calls : There are 5 different categories of
system calls –
 Process control: end, abort, create, terminate, allocate and free
memory.
 File management: create, open, close, delete, read file etc.
 Device management
 Information maintenance
 Communication
4/27/2020 Prof. Arti Gavas 41

42. Examples of Windows and Unix System Calls
WINDOWS UNIX
Process Control
CreateProcess()
ExitProcess()
WaitForSingleObject()
fork()
exit()
wait()
File Manipulation
CreateFile()
ReadFile()
WriteFile()
CloseHandle()
open()
read()
write()
close()
Device
Manipulation
SetConsoleMode()
ReadConsole()
WriteConsole()
ioctl()
read()
write()
Information
Maintenance
GetCurrentProcessID()
SetTimer()
Sleeo()
getpid()
alarm()
sleep()
Communication
CreatePipe()
CreateFileMapping()
MapViewOfFile()
pipe()
shmget()
mmap()
Protection
SetFileSecurity()
InitlializeSecurityDescriptor()
SetSecurityDescriptorGroup()
chmod()
umask()
chown()
4/27/2020 Prof. Arti Gavas 42

43. Operating System Structure
• The design of an operating system architecture traditionally
follows the separation of concerns principle.
• This principle suggests structuring the operating system into
relatively independent parts that provide simple individual
features, thus keeping the complexity of the design
manageable.
4/27/2020 Prof. Arti Gavas 43
Simple Structure
Monolithic Systems
Layered Systems
Microkernel Systems
Virtualized Systems

44. Simple Structure
• Operating systems such as MS-DOS and the original UNIX did
not have well-defined structures.
• There was no CPU Execution Mode (user and kernel), and so
errors in applications could cause the whole system to crash.
4/27/2020 Prof. Arti Gavas 44

45. Monolithic Systems
• Functionality of the OS is invoked with simple function calls
within the kernel, which is one large program.
• Device drivers are loaded into the running kernel and become
part of the kernel.
4/27/2020 Prof. Arti Gavas 45

46. Layered Systems
• his approach breaks up the operating system into different
layers.
• This allows implementers to change the inner workings, and
increases modularity.
• As long as the external interface of the routines don’t change,
developers have more freedom to change the inner workings of
the routines.
• With the layered approach, the bottom layer is the hardware,
while the highest layer is the user interface.
• The main advantage is simplicity of construction and
debugging.
• The main difficulty is defining the various layers.
• The main disadvantage is that the OS tends to be less efficient
than other implementations.
4/27/2020 Prof. Arti Gavas 46

47. Layered Systems
4/27/2020 Prof. Arti Gavas 47

48. Microkernels
• This structures the operating system by removing all
nonessential portions of the kernel and implementing them as
system and user level programs.
• Generally they provide minimal process and memory
management, and a communications facility.
• Communication between components of the OS is provided by
message passing.
• The benefits of the microkernel are as follows:
 Extending the operating system becomes much easier.
 Any changes to the kernel tend to be fewer, since the kernel is
smaller.
 The microkernel also provides more security and reliability.
• Main disadvantage is poor performance due to increased
system overhead from message passing.
4/27/2020 Prof. Arti Gavas 48

49. Microkernels
4/27/2020 Prof. Arti Gavas 49

50. Virtualized Systems
• In computing, virtualization means to create a virtual version of
a device or resource, such as a server, storage device, network
or even an operating system where the framework divides the
resource into one or more execution environments.
• Even something as simple as partitioning a hard drive is
considered virtualization because you take one drive and
partition it to create two separate hard drives.
• It is an attempt to simplify maintenance and improve utilization
of operating systems that host multiple independent
applications have lead to the idea of running multiple operating
systems on the same computer.
• Similar to the manner in which the operating system kernel
provides an isolated environment to each hosted application,
virtualized systems introduce a hypervisor that provides an
isolated environment to each hosted operating system.
4/27/2020 Prof. Arti Gavas 50

51. Client/server architecture of operating system
• A trend in modern operating system is to move maximum code
into the higher level and remove as much as possible from
operating system, minimizing the work of the kernel.
• The basic approach is to implement most of the operating
system functions in user processes to request a service, such
as request to read a particular file, user send a request to the
server process, server checks the parameter and finds whether
it is valid or not, after that server does the work and send back
the answer to client server model works on request- response
technique
• i.e. Client always send request to the side in order to perform
the task, and on the other side, server gates complementing
that request send back response.
4/27/2020 Prof. Arti Gavas 51

52. Exokernel
• Exokernel is an operating system developed at the Massachusetts Institute of
Technology that seeks to provide application-level management of hardware
resources.
• The exokernel architecture is designed to separate resource protection from
management to facilitate application-specific customization.
• Exokernels are typically small in size because of their limited operability.
• Some of the features of exokernel operating systems include:
 Better support for application control
 Separates security from management
 Abstractions are moved securely to an untrusted library operating system
 Provides a low-level interface
 Library operating systems offer portability and compatibility
• The benefits of the exokernel operating system include:
 Improved performance of applications
 More efficient use of hardware resources through precise resource allocation and
revocation
 Easier development and testing of new operating systems
 Each user-space applications is allowed to have to apply its own optimized
memory management
• Some of the drawbacks of the exokernel operating system include:
 Reduced consistency
 Complex design of exokernel interfaces
4/27/2020 Prof. Arti Gavas 52

53. Question Bank
4/27/2020 Prof. Arti Gavas 53
1) What is operating system? Explain with its four
components.
2) Why do we need Operating System?
3) Explain Types of Operating Systems.
4) Briefly explain Monolithic architecture of OS.
5) What is a system call? Explain its types.
6) What are the benefits of Exokernel?
7) Explain Disk.
8) What is booting a computer system?
9) What is a process?
10) What are the common services provided by OS?