Chapter - 1, Operating System, Computer Science Key Point Notes, HSSC-II (12th Class)

12th Class (HSSC-II) Computer SLO Based Key Point Notes

(National Book Foundation - As Federal Textbook Board, Islamabad
Based on National Curriculum Pakistan 2024-2025 and Onward prescribed by Federal Board of Intermediate and Secondary Education, Islamabad, and All Pakistan Boards)

Unit 1: OPERATING SYSTEM

1.1.1 Introduction to Operating System:

It is a program that controls and coordinates all the functions of the computer system. It acts as an interface between the user and the hardware. It performs the following tasks:

Load software into main memory and execute it.
Control the operation of the main memory.
Manage files and folders on storage devices.
Manage the operations of I/O devices.
Allows multitasking to handle several tasks at the same time.
Provides security through password and username.
Performs network operations.
Detect hardware failure.

Block Diagram of Functions of Operating System:

1.1.2 Commonly Used Systems or Types of Operating Systems or

DOS operating system

DOS stands for Disk Operating System.

WINDOWS Operating System

It was developed in the mid-1980s by Microsoft Corporation.

DOS vs WINDOWS

Mac OS

It is a series of operating systems developed by

UNIX

It was developed in the early 1970s at the Bell Lab. research center

1.1.3 Types of Operating Systems

Batch Processing Operating System

A Batch-processing OS groups together the same type of jobs in batches and automatically executes them one by one.

Multiprogramming Operating System

It is software that loads one or more programs in the main memory and executes them using a single CPU.

Multitasking Operating System

It is software that performs multiple tasks at the same time on a computer that has a single CPU.
The CPU executes only one program at a time but it rapidly switches between multiple programs and it appears as if all the user's programs are being executed at the same time.
For Example, the user can edit a text document while a webpage is being loaded in the browser.

Time-Sharing Operating System

It is software that shares the CPU time between multiple programs that are loaded in the main memory.
It gives a very short period of CPU to each program which is called time slice or quantum.
It is used in mini and mainframe computers that support a large number of users.
These computers support a large number of users in big organizations such as Airlines, Banks, etc.

Real-Time Operating System

It is software that runs a real-time application that must process data as soon as it comes and provides an immediate response.
They are used in the fields where a quick response is critical.
Some applications of real-time operating systems are as follows:
It is commonly used in space research programs
Real-time traffic control and control of industrial processes such as oil refining.
Automated Car Assembly Plant.
Air traffic system.
Heart Pacemaker system.
Scientific experiments for Nuclear reactors.
Medical Science application(Magnetic Resonance Imaging (MRI) Scan, Radiation therapy).
Defense applications(Missile guidance system, anti-missile system, Satellite missile system), etc.

Multiprocessor Operating System

It is software that controls the operations of two or more CPUs within a single computer system.
All CPUs share the same memory and I/O devices.
It is used to obtain very high speed to process large amounts of data.
It executes a single program using many CPUs at the same time.
It improves the processing speed.
The computer needs complex architecture to support multiprocessing.

Parallel Processing Operating System

It is software that executes programs developed in a parallel programming language.
It uses many processors at the same time.
It divided the task of a program into many smaller tasks and processed them on multiple processors at the same time.
It is used in Supercomputers that have thousands of processors.

Distributed Operating System

It is software that manages the operation of a distributed system which allows the execution of applications software on different computers in a network.
In a distributed system, user programs may run on any computer and access data on any other computer in the network and users of a program do not know on which computer their programs are running.

Embedded Operating System

It is a built-in operating system that is embedded in the hardware of the device that controls the functions of the device such as Microwave oven, TV, ATM, Digital Camera, Washing machines, Games, etc.
It runs automatically when the device is turned on and performs a specific task.

1.1.4 Single User and Multiuser Operating Systems

Single User Operating System:

Example: DOS, WINDOWS

Multiuser Operating System:

It allows many users on different microcomputers to use the resources of a single central computer (Server) in a network.

1.2 Operating System Functions

1. Process Management

A process is a program in execution.

2. Memory Management

It is a part of the OS that controls and manages the operations of main memory.

3. File Management

It is a part of the OS that manages files and folders on storage devices such as hard disks, USB flash drives CDs/DVD,s etc.
It allows the users to perform operations such as copying, creating, moving, renaming deleting, and searching files and folders.
It also allows the user to perform read, write open, and close operations on file folders.

4. I/O Management

It is the part of OS that controls all the I/O operations during program execution.
It manages all the INPUT/OUTPUT operations of I/O and storage devices.
The user communicates with a computer with different I/O devices i.e. Keyboard, Mouse, Monitor, etc.
It also detects and handles errors during data transmission.

5. Secondary Storage Management

It is the part of the OS that manages free space and storage allocation of user programs and data on secondary storage devices.
It also allocates and deallocates the storage space to user programs.

6. Network Management

It is the part of OS the that monitors and manages the resources of a network.
It allows to creation of user groups and assigns privileges to them.
It shares the network resources among users and detects and fixes network problems.

7. Protection System

It is the part of the OS that ensures

8. Command Interpreter

It is part of the OS that provides an interface between the user and the computer system.
It is a file in OS that reads and executes user commands entered as text through the keyboard.
For example, WINDOWS OS uses the cmd.exe file as a command interpreter.

1.3. Process Management

1.3.1 Process Definition:

A process is a program in execution.

1.3.2 Various States of a Process

• There are five states of a process which are shown in the figure:

1. NEW state:

This is the first state of a process when it is created.

2. READY state:

A process is said to be in a ready state when it is ready for execution but waiting to be assigned to the CPU by OS.

3. RUNNING state:

A process is said to be in a running state when it is being executed by the processor.

4. BLOCKED state:

A process is in the blocked or waiting state when it is not under execution and waiting for a resource to become available.

5. TERMINATED state:

A process is in the terminated state when it completes its execution.

1.3.3 Thread and Process

Process:

A process is an executable instance of a program.

Thread:

– A thread is a sequence of instructions within a process that executes independently.
– Threads are created and exited within a process.

Process vs Thread 👇

1.3.4 Multithreading:

The process of executing multiple threads simultaneously is known as Multithreading.
It is an execution method of a program that allows a single process to run multiple threads at the same time.
The main purpose of multithreading is to provide simultaneous execution of two or more parts of a program to maximum utilize the CPU time.

1.3.5 Multitasking:

Multitasking is the function of the operating system that loads multiple tasks in the main memory and executes them at the same time by rapidly switching the CPU among them.

1.3.6 Multiprogramming:

Many programs are loaded in memory but the CPU only executes one program at a time.
The advantage of multiprogramming is that it saves the user’s time in loading the program to the main memory and runs the program quickly.
The only drawback is, that the system requires more memory as it is occupied by many programs.
Some bigger programs cannot load fully in memory and thus programs run slowly.

Multiprocessing:

It is the ability of an OS to execute more than one process on a multi-processor machine at the same time.

Multiprogramming vs Multitasking

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