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Unit I: Introduction and Operating Systems structures
Evolution of operating systems: Batch, timesharing, multiprogramming, multi-tasking and
distributed and real time.
Operating system components
O.S. Services
System Calls
System Programs
System Structure
Virtual Machines
Special purpose operating systems
Open-source operating systems
Boot Procedure
Overview of the GNU/Linux system administration.

• An operating system (OS) consists of several components that work together to
manage computer hardware resources and provide a platform for running
applications. The main components of an operating system are:
1. Kernel: The core of the OS, responsible for managing hardware resources,
process scheduling, and memory management.
2. Device Drivers: Software components that allow the OS to interact with hardware
devices such as printers, graphics cards, and sound cards.
3. System Calls: Interfaces that allow applications to request services from the OS,
such as process creation, file access, and network communication.
4. System Libraries: Pre-built software libraries that provide common functions and
services to applications, such as input/output operations and data management.
5. User Space: The area of the system where applications run, isolated from the
kernel and other system components.

6. Command Interpreter (Shell): A program that allows users to interact with the OS
using commands and instructions (e.g., Windows Command Prompt, Linux
Terminal).
7. Graphics User Interface (GUI): A visual interface that allows users to interact
with the OS using graphical elements like windows, icons, and menus (e.g.,
Windows, macOS, Linux desktop environments).

Operating System Services
Operating system services refer to the functionality and features provided by an
operating system to enable applications to interact with the computer hardware and
other system resources. Some common operating system services include:
1. Process Management: Creating, running, and managing processes (programs) and
threads.
2. Memory Management: Allocating and deallocating memory for programs.
3. File System Management: Providing access to files, directories, and storage devices.
4. Input/Output (I/O) Management: Managing input from devices like keyboards and
mice, and output to devices like printers and monitors.
5. Security: Controlling access to system resources, enforcing permissions, and
protecting against malware.
6. Networking: Managing communication between the computer and other devices on
a network.7. Interrupt Handling: Managing interrupts generated by hardware devices

Structure of a Computer System
A computer system can be divided roughly into four components:
Hardware
Operating system
Application programs
The users
In the Computer System, Hardware can only understand machine code (in the form of 0 and 1) which doesn't
make any sense to a naive user.
We need a system which can act as an intermediary and manage all the processes and resources present in the
system.
What is Operating System:
Operating system is a group of programs that manages and control all operations of computer system and act as
an interface between user and computer system.

Operating system as a Resource Allocator
A computer system has many resources that may be required to solve a problem:
CPU time,
memory space,
file-storage space
I/O devices, and so on.
The operating system acts as the manager of these resources
Facing numerous and possibly conflicting requests for resources, the operating system must decide how to
allocate them to specific programs and users so that it can operate the computer system efficiently and
fairly.

Types of Operating Systems (OS)/ Evolution of operating systems
1.Batch Operating System
2.Multiprogramming Operating System
3.Multiprocessing Operating System
4.Multitasking Operating System
5.Network Operating System
6.Real Time Operating System
7.Time-Sharing Operating System
8.Distributed Operating System

Batch Operating System
Batch processing – 1970’s
A single computer which was called a mainframe
Similar types of jobs were batched together and exec-
uted in time
Access is given to more than one person
They submit their respective jobs to the system for the execution
The system put all of the jobs in a queue on the basis of first come first serve and executes the jobs one by
one.
The users collect their respective output when all the jobs get executed.
The purpose of this operating system was mainly to transfer control from one job to another as soon as the
job was completed
It contained a small set of programs called the resident monitor that always resided in one part of the main
memory.

Advantage:
The use of a resident monitor improves computer efficiency as it eliminates CPU time between two jobs
Disadvantage:
Batch processing suffers from starvation
Not Interactive : Batch Processing is not suitable for jobs that are dependent on the user's input

Multiprogramming Operating System
• Multiprogramming is an extension to batch processing where the CPU is always kept busy. Each process
needs two types of system time: CPU time and IO time.
• In a multiprogramming environment, when a process does its I/O, The CPU can start the execution of
other processes. Therefore, multiprogramming improves the efficiency of the system.

Advantages of Multiprogramming OS
Throughput is increased as the CPU always had one program to execute
Response time can also be reduced.
Disadvantages of Multiprogramming OS
Systems resources are used efficiently, but they do not provide any user interaction with the computer system

Multiprocessing Operating System
In Multiprocessing, Parallel computing is achieved. There are more than one processors present in the system
which can execute more than one process at the same time.
Advantages:
Increased reliability
Increased throughout
Disadvantages:
Complex as it takes care of multiple CPUs simultaneously

Multitasking Operating System
Logical extension of a multiprogramming system that enables
multiple programs simultaneously
It allows a user to perform more than one computer task at the
same time
Advantages:
Supports multiple users simultaneously
Have well-defined memory management
High Reliability
Optimized Computer Resources
Disadvantages:
Memory Limitations
CPU Overheating

Network Operating System
An Operating system, which includes software and associated protocols to communicate with other computers
via a network conveniently and cost-effectively, is called Network Operating System
Advantages:
Network traffic reduces due to the division between clients and the server
less expensive to set up and maintain
Disadvantages:
The failure of any node in a system affects the whole system
Security and performance are important issues
So trained network administrators are required for network administration

Real Time Operating System
In Real-Time Systems, each job carries a certain deadline within which the job is supposed to be completed,
otherwise, the huge loss will be there, or even if the result is produced, it will be completely useless
Advantages:
Maximum utilization of devices and systems
Disadvantages:
Very costly to develop
Very complex and can consume critical CPU cycles.

Time-Sharing Operating System
In the Time Sharing operating system, computer resources are allocated in a time-dependent fashion to several programs
simultaneously
Provides a large number of user's direct access to the main computer
It is a logical extension of multiprogramming
The CPU is switched among multiple programs given by different users
Advantages:
Provides effective utilization and sharing of resources
reduces CPU idle and response time
Disadvantages:
Data transmission rates are very high in comparison to other methods
Very difficult and expensive to build
Security and integrity of user programs loaded in memory and data need to be maintained as many users access the system
at the same time

Distributed Operating System
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.
Advantages:
Provides sharing of resources
Load Balancing
System is fault-tolerant
Disadvantages:
Lack of Centralized Control
Data Inconsistency
Communication Overhead

Input
Output
Memory
CPU
The components of an operating system play a key role to make a variety of computer system parts work
together. There are the following components of an operating system, such as:
Process Management I/O Device Management
File Management Network Management
Main Memory Management Security and Protection Management
Secondary Storage Management Error Detection

1.Operating System-unit 1.pptx Evolution of operating systems: Batch, timesharing, multiprogramming, multi-

Process Management :
• A process is a program in execution. It consists of the followings:
The operating system is responsible for the following activities in connection with process management:
Creating and deleting both user and system processes
Suspending and resuming processes
Providing mechanisms for process synchronization
Providing mechanisms for process communication
Providing mechanisms for deadlock handling

File Management:
Following are the major activities of an operating system with respect to file management −
Creating and deleting files
Creating and deleting directories to organize files
Supporting primitives for manipulating files and directories
Mapping files onto secondary storage
Backing up files on stable (nonvolatile) storage media
I/O Device Management
An I/O subsystem comprises of I/O devices and their corresponding driver software
Drivers hide the peculiarities of specific hardware devices from the users
An Operating System manages the communication between user and device drivers
I/O operation means read or write operation with any file or any specific I/O device.
Operating system provides the access to the required I/O device when required

Network Management
Network management is a fundamental concept of computer networks
Network Management Systems is a software application that provides network administrators with
information on components in their networks.
It ensures the quality of service and availability of network resources.
It also examines the operations of a network, reconstructs its network configuration, modifies it for
improving performance of tasks.
Main Memory management
Used to keep track of the status of memory locations, whether it is free or allocated.
Permits computers with a small amount of main memory to execute programs larger than the size or amount
of available memory.
Responsible for protecting the memory allocated to each process from being corrupted by another process.
Memory managers should enable sharing of memory space between processes.

Security and Protection
It refers to a mechanism or a way to control the access of programs, processes, or users to the resources defined
by a computer system
Following are the major activities of an operating system with respect to protection
The OS ensures that all access to system resources is controlled
The OS ensures that external I/O devices are protected from invalid access attempts
The OS provides authentication features for each user by means of passwords
Secondary Storage Management
Responsible for allocating blocks to files
Must keep track of space available for allocation

Error Detection
Errors can occur anytime and anywhere
A mistake may occur within the CPU, in I/O devices or the memory hardware
The OS constantly checks for possible errors
The OS takes applicable legal action to make sure accurate and reliable computing

System Calls
System calls provide an interface to the services made available by an operating system
A system call is a mechanism used by programs to request services from the operating system (OS)
Types of System Calls
System calls can be grouped roughly into six major categories: process control, file manipulation, device
manipulation, information maintenance, communications, and protection.

Operating System Structure: There are six designs
Monolithic systems
Layered systems
Microkernels
Client-server systems
Virtual machines
Exokernels
Monolithic systems
The operating system kernel is designed to provide all operating system services, including memory management, process
scheduling, device drivers, and file systems, in a single, large binary
This means that all code runs in kernel space, with no separation between kernel and user-level processes
Each procedure in the system is free to call any other one, if the latter provides some useful computation that the former needs
Also, a crash in any of these procedures will take down the entire operating system

Advantages
High performance, Simplicity,
Low overhead, Fast system calls,
Easy to develop drivers etc
Disadvantages
Large and complex applications, Slow development,
Unscalable, Unreliable, Inflexible
Characteristics
Single Executable :All components and modules are bundled together
Tight Coupling: All modules are interconnected and dependent on each other
Shared Memory: Can directly access and modify shared data structures.
Monolithic Deployment: Entire application is deployed as a single unit
Centralized Control Flow: Control flow within the application is typically managed by a central module

Layered Approach
To organize the operating system as a hierarchy of layers, each one constructed upon the one below it.
The system had six layers: The bottom layer (layer 0) is the hardware; the highest (layer N) is the user interface.
Layer 0 dealt with allocation of the processor, switching between processes when interrupts occurred or timers
expired. In other words, layer 0 provided the basic multiprogramming of the CPU.
Layer 1 did the memory management. It allocated space for processes in main memory and on a 512K word
drum used for holding parts of processes (pages) for which there was no room in main memory.
Layer 2 handled communication between each process and the operator console
Layer 3 took care of managing the I/O devices and buffering the information streams to and from them.
Layer 4 was where the user programs were found.
The system operator process was located in layer 5.

Advantages
Easy Debugging
Modularity
Abstraction
Easy Update
Disadvantages
Complex
Slower in execution

Layered Approach
To organize the operating system as a hierarchy of layers, each one constructed upon the one below it.
The system had six layers:
Layer 0 dealt with allocation of the processor, switching between processes when interrupts occurred or timers
expired. In other words, layer 0 provided the basic multiprogramming of the CPU.
Layer 1 did the memory management. It allocated space for processes in main memory and on a 512K word
drum used for holding parts of processes (pages) for which there was no room in main memory.
Layer 2 handled communication between each process and the operator console
Layer 3 took care of managing the I/O devices and buffering the information streams to and from them.
Layer 4 was where the user programs were found.
The system operator process was located in layer 5.
https://os.ecci.ucr.ac.cr/slides/Abraham-Silberschatz-
Operating-System-Concepts-10th-2018.pdf
https://drive.uqu.edu.sa/_/mskhayat/files/MySubjects/2017SS
%20Operating%20Systems/Abraham%20Silberschatz-Operating
%20System%20Concepts%20(9th,2012_12).pdf

• Some operating systems are created for special purposes, like:
1. Firewalls:
 A network security device that monitors incoming and outgoing network traffic and decides
whether to allow or block specific traffic based on a defined set of security rules.
2.Routers
A router is a device that connects two or more packet-switched networks or subnetworks. It
serves two primary functions: managing traffic between these networks by forwarding data
packets to their intended IP addresses, and allowing multiple devices to use the same Internet
connection.
3.Phones
mobile telephone, portable device for connecting to a telecommunications network in order to
transmit and receive voice, video, or other data.
4.ATM machines
An automated teller machine (ATM) is an electronic telecommunications device that enables
customers of financial institutions to perform financial transactions, such as cash withdrawals,
deposits, funds transfers, balance inquiries or account information inquiries, at any time

• A special type of operating system is a real-time operating system (RTOS)
• Guarantee to perform tasks in a predefined amount of time
• Used where handling events within a predefined time is critical
• Factories
• Power plants
• Vehicles
• Example: QNX
QNX is a commercial Unix-like real-time operating system owned by BlackBerry, aimed
primarily at the embedded systems market.
QNX, initially released by Quantum Software Systems – later renamed QNX Software
Systems – in 1982 was one of the first commercially successful microkernel operating systems.

• What is an Open-Source Operating System?
The term "open source" refers to computer software or applications where the owners or
copyright holders enable the users or third parties to use, see, and edit the product's source
code.
The source code of an open-source OS is publicly visible and editable. The usually operating
systems such as Apple's iOS, Microsoft's Windows, and Apple's Mac OS are closed operating
systems.
The open-source operating system allows the use of code that is freely distributed and
available to anyone and for commercial purposes. Being an open-source application or
program, the program source code of an open-source OS is available.
The user may modify or change those codes and develop new applications according to the
user requirement. Some basic examples of the open-source operating systems are Linux,
Open Solaris, Free RTOS, Open BDS, Free BSD, Minix, etc.

• Best Open-Source Operating System
• Most of the open-source operating systems are Linux based. Some of the
best open-source operating systems are as follows:
• 1. Linux Kernel
Linux kernel was developed by Linus Torvalds.
It offers the essential functions required for an operating system, such as
data cancellation, memory processing, and interactions with computer
hardware.
It is open-source software, and many developers researched the source
code.

2. Linux Lite
Linux Lite is another free and open-source operating system that can run on lower-end hardware.
It is a lightweight operating system designed to help users who are unfamiliar with Linux-based
operating systems.
The operating system includes all of the required programs, capabilities, tools, and desktops.
 It has a minimal interface and is entirely based on the Ubuntu system. In the last five years, the
operating system has been stable and has received regular updates.
 It is efficiently functional soon after installation. After installation, users are not required to
install any further drivers.
If you want a lightweight open-source operating system on your PC, go with Linux Lite.

3. Linux mint
Linux Mint is a powerful Linux-based operating system that exudes modernity and
power.
It is simple to use and includes complete multimedia capabilities, making it a user-
friendly open-source operating system.
It is an Ubuntu-based distribution that is popular among both beginners and experts
It is built on the Debian platform and includes one of the most powerful software
managers.
 It is more stable and has better visual aesthetics than Ubuntu.

4. Fedora
Fedora is another popular Linux-based operating system, and it is widely considered the best
open-source operating system after Ubuntu.
It is an RPM-based(Red-hat Package Manager) general-purpose operating system that is supported
by Red Hat and built by the Fedora Project community.
Its purpose is to develop and share cutting-edge open-source technology for free.
 Fedora developers' updates are available to all Linux distributions.

5.React OS
ReactOS is another free and open-source operating system that has nearly 1
million downloads in over 100 countries.
This community-based OS may run Windows apps, making it an excellent
alternative to the Windows operating system.
Although ReactOS is still growing, users, who love highly customizable
operating systems, can select ReactOS. However, the operating system is developer-
focused.

6. Solus
Solus is a free and open-source operating system for your desktop computer.
It's a new operating system from the Linux family, released in 2012. More
than 6000 registered users are currently using the software.
VLC, XChat, Transmission, Thunderbird, OpenShot Video Editor, Firefox,
Budgie desktop environment, and LibreOffice Suite are all included with Solus.
The most recent version of Solus, Solus 3, was released in August 2017.

7. Chrome OS
Chrome OS is a partly open-source operating system with various attractive
features.
It's a part of the Chromium and Linux families, with features including better
security, compatibility for supported Android and Chrome apps, Aura windows
manager, Google cloud print, integrated media player, virtual desktop access, and
cloud-based management.
The only issue with the operating system is that it only supports Nexus devices or
its hardware. As a result, if you're a Google fan, you'll love Chrome OS on a
Chromebook.

•Advantages
1. Reliable and efficient
The open-source operating systems are most reliable and efficient. Thousands of eyes monitor these
because the source code is public. As a result, if there are any bugs or errors, they are fixed by the
best developers worldwide.
2. Cost-efficient
Most of the open-source operating systems are free. And some of them are far less expensive than
commercially closed products.
3. Flexibility
The great advantage is you may customize it as per your requirement. And there is creative freedom.

•Disadvantages
1. Complicated
It is not as user-friendly as the ones that are closed. To use this software, you must
have a basic understanding of technology.
2, Security risk
Despite the defects having been detected, there is a risk of assaults because the
attackers have access to the source code.
3. No support
If you run across an issue, there is no customer support available to assist you.

Boot Procedure
Booting is basically the process of starting the computer.
When the CPU is first switched on it has nothing inside the Memory.
In order to start the Computer, load the Operating System into the Main Memory and
then Computer is ready to take commands from the User.
Types of Booting:
There are two types of booting:
1. Cold Booting
A cold boot is also called a hard boot. It is the process when we first start the computer.
In other words, when the computer is started from its initial state by pressing the power
button it is called cold boot.
 The instructions are read from the ROM and the operating system is loaded in the
main memory.

Boot Procedure
1. Warm Booting
Warm Boot is also called soft boot. It refers to when we restart the computer.
Here, the computer does not start from the initial state.
 When the system gets stuck sometimes it is required to restart it while it is ON.
Therefore, in this condition the warm boot takes place. Restart button or
CTRL+ALT+DELETE keys are used for warm boot.

Boot Procedure
Steps of Booting
• We can describe the boot process in six steps:
1. The Startup
It is the first step that involves switching the power ON. It supplies electricity to
the main components like BIOS and processor.
2. BIOS: Power On Self Test
It is an initial test performed by the BIOS. Further, this test performs an initial
check on the input/output devices, computer’s main memory, disk drives, etc.
Moreover, if any error occurs, the system produces a beep sound.
3. Loading of OS
In this step, the operating system is loaded into the main memory. The operating
system starts working and executes all the initial files and instructions.

Boot Procedure
Steps of Booting
4. System Configuration
In this step, the drivers are loaded into the main memory. Drivers are programs
that help in the functioning of the peripheral devices.
5. Loading System Utilities
System utilities are basic functioning programs, for example, volume control,
antivirus, etc. In this step, system utilities are loaded into the memory.
6. User Authentication
If any password has been set up in the computer system, the system checks for
user authentication.
 Once the user enters the login Id and password correctly the system finally starts.

Comparison of various operating systems
1. Windows-
Pros:
- User-friendly interface
- Wide software compatibility
- Strong gaming support-
Cons:
- Resource-intensive
- Vulnerable to malware
- Can be expensive

2. macOS
Pros:
- High-performance capabilities
- Strong security features
Cons:
- Limited software compatibility
- Expensive hardware requirements
- Not compatible with PC hardware

3. Linux-
Pros:
- Open-source and free
- Highly customizable
- Strong security features
- Fast performance-
Cons:
- Steep learning curve
- Limited gaming support
- Some software compatibility issues

4. Chrome OS-
Pros:
- Fast, lightweight performance
- Easy to use
-Affordable hardware options
- Strong web-based application support-
Cons:
- Limited offline capabilities
- Limited software compatibility
- Not suitable for heavy productivity tasks

5. Android-
Pros:
- Wide range of hardware options
- Customizable interface
- Strong app ecosystem
- Affordable
Cons:
- Fragmented ecosystem
- Security concerns
- Not suitable for heavy productivity tasks

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