Operating System

Operating System

Introduction To Operating System

Basics Of Operating System

An Operating System is a type of  system software and a crucial component of every computer system.  The Operating system ( OS ) functions as an interface between application software and the computer hardware . 

The OS provides an user friendly interface to the system user to perform various operations on the computer system.

Operating system performs some of the most crucial functions such as resource allocation management, system security, command interpreter, file management, communication with hardware components and, input and output management.

Operating System

In this article , you will learn what is operating system , OS important functions, features, different types of OS  and modes , components of OS and its architecture, OS booting process, program execution, processes management and other important topics related to the OS.

What is Operating System ?

Definition Of Operating System ?

An operating system (OS) is a software program that acts as an intermediary between users and computer hardware. It manages hardware resources such as the CPU, memory, and storage devices, and provides services that allow applications to run smoothly.

The OS handles tasks such as managing files, running programs, and controlling input/output devices. It also provides a user interface, allowing users to interact with the computer system and perform tasks such as launching programs, managing files, and configuring settings.

Overall, the operating system is essential for the functioning of a computer, enabling users to use and control hardware resources effectively and providing a platform for running applications.

What Is Operating System ?

The Operating System ( OS ) is an essential component of every computer system . The computer system cannot function without the operating system .

And therefore , when the computer system is powered on , the CPU’s first task is to load the operating system . The computer system becomes fully operational to the user only after the OS is loaded into the main system memory .

A  Computer System   consist   of  two  main  components   : 

  1. Hardware   Components 
  2. Software   Components  .

The  Software components consist  of  system software  and  application  software  .  The   application  programs which provides an interface to the user  cannot  directly interact with  the hardware components .

And  therefore ,  the system needs  a  special  system  program  called “Operating System”  which  can  interact  with  the  hardware components.

The OS internally use another system software called driver. The operating system interacts with hardware components  through  a  set  of  drivers  (  another system program ). The OS    manages  all  application  programs  and   system  resources .

Software Engineering , What is Software , SDLC
Software Engineering , What is Software , SDLC

An  operating system  ( OS )  is the most important software  component of a computer system which provides the necessary  resources  and the run-time environment to various  other  applications  running  on the  computer .

    An  OS  is system software that manages the computer hardware , software applications  , system resources such as memory  and  provides  common services  to   the   computer programs .

The operating system is the overall in charge of the computer system . The OS also has access to all the critical functions and the resources managed by the computer system. 

In order to effectively perform this role , the  OS performs  some of the most important  functions  for  managing  the software  and  hardware resources  of the system .  

Operating System Functions

Process Management

The computer user generally works in a multi tasking environment . For example the user might  simultaneously open two or more ms word document or open multiple web pages in a browser  .

Each of this open document represent a process . The OS initiates the program execution by loading an executable copy of the  program into the main memory RAM .

In other words , In  computing , a process is an instance of a computer program  that  is  being  currently  executed . Each open MS word document active in the system memory  represents an instance of program .

A typical computer program consist of number of program instructions . During the program execution , the OS allocates resources and the CPU starts executing these program instructions.

A  process  is the actual execution of these program  instructions when  Operating System  allocates the  resources   (  Memory  and  processor  time ) . The OS handles several processes running simultaneously and associated  with  the  same   program . 

For Example :   A user may working on number of  MS word documents  simultaneously  .

Operating System Process Management

A  process can be user application program Or system process . The OS is responsible  to  manage  both these  processes .

A   multitasking   operating system   rapidly  switches   the  CPU execution time   between the different processes  currently being executed . 

Although  , the CPU  executes  only one process at a time  but  due to  rapid switching between the processes in queue ,    it  creates  an  illusion  that  all  programs ( processes )  are   running   simultaneously  but   actually CPU executes only one process at a time. 

Process Management Diagram

The process management is an important function managed by the operating system . The  CPU  can execute  only one process  at a time . And therefore,  The OS  has to decide  the  schedule for the process execution .

This schedule includes  the order of execution for different  processes in pipeline  at  various  stages of their execution  and  the CPU time  to  be  allocated  .    

Process Status Diagram

Operating System Process Status Diagram

Memory Management

The Operating System ( OS ) loads the program to be executed in to the main system memory RAM . The system memory is a limited resource that is managed by the OS . The program execution needs resources in terms of memory and the CPU’s processing time .

The operating system  manages the memory of the computer system by allocating main memory to  different process currently under execution at various stages .

The OS is also responsible main memory to reallocated  the memory from the process  that  is  already  terminated .  The system memory is an important   resource  and  the OS  manages  this  by  allocation to new processes  and  by reallocating  the memory  from  terminated processes. 

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What Is Computer Memory ?

Random Access Memory

Virtual Memory

Operating System Memory Management

For  a computer  system , the main memory RAM will always be a limited resource  due to ever  increasing  size of the software  and  the number of programs   simultaneously  running  on  the system .

The OS solves this problem with the help of mechanism called the  virtual memory . The virtual memory  solves this problem by converting a part of secondary memory into virtual addresses thereby creating a  large size of the RAM  to accommodate the increased memory requirement.

The Operating system ( OS )  translates these virtual addresses into physical addresses.

Operating System Memory Management Virtual Memory

What Is Virtual Memory ?

The  Computer system memory unit  consist of different types of memory arranged in hierarchical  order . Each  memory performs specific function  and optimally  used by the OS  during  various  stages of  program execution  . 

The  virtual  memory  is  a critical mechanism  which  allows the  OS  to use  some portion of the disk memory ( Secondary Memory )  as logical  extension  of the main system memory  RAM . Thereby allowing  execution  of the programs that exceeds  the  available  size of the  available RAM .


What Is Virtual Memory ?

System Resource Management

The resource management is one of the important function handled by the OS. The OS is the overall in-charge of the system resources . Some of the most important system resources include the main system memory RAM , Storage space and the processor cycle time .

The CPU starts the program execution when the operating system loads the executable copy of the program into the main system memory RAM . 

The OS allocates the required memory  to execute the program . The OS also allocates another important resource that is CPU’s processing time .

The computer system may be equipped with multi-core processor where each core functions as an independent processor . This complexity is more in a network environment where system resources are shared by many users.  

The OS handles this complex operation of allocating and deallocation the resources amongst different processes running on the system and at different stages of execution.

Security Management

One of the important responsibility of the operating system is to provide  secure and protected run-time environment to  the various   process ( both application process and system processes )   which   are  being  executed  on the computer system  . 

The System  security  is  another important  aspect  which is handled by  the  OS  . Protecting  system  against  unauthorized  access  can  be implemented  by  activating  different   security  features  of  the  OS . 

Security Manager
Security Management

Command Interpreter

A  command interpreter is a crucial component of the OS and it is a  program   which   reads  the  instructions  given  by  the  user. The command interpreter then translates these  instructions  into  the  context  of the OS followed by its  execution. The Command interpreter is also  known as  “shell’. 

 A  command interpreter is the part of a computer operating system that interprets  and executes commands that  are  entered  interactively  by the system user or from a application program. In some operating systems ( OS ), the command interpreter  is  commonly referred as “‘shell’.

Operating System Command Interpreter
Command Interpreter

A   command interpreter  is an interface between system and  the user.  There  are  two  types  of user interface  :

1. Command Line  Interface.  

2.Graphical User Interface  (  GUI  ).

Command Line :  With a command line user interface the user interact with the  Operating System  by  typing commands  to  perform specific  tasks .

GUI  Interface : With a  graphical user interface ( GUI ) the user interacts with  the Operating System  by using  a mouse to access windows icons  and menus .

File Management

The file management is one of the basic and important features of the operating system ( OS ) . 

The OS is responsible to manage the files in a  computer system. All the files with different extensions are managed by the  OS. The User interacts with the OS to perform various file operations.

A   file  is a collection of  related information . A file can be a text file , image , audio , video and may contain data in any other form . 

The OS presents the information to the user through GUI user friendly interface . However , the  data  is  represented  in a computer  system  only  in  a  binary  form  (  0  and  1 ) .

File Management
File Management Logical View

The  data  is  stored permanently in a  secondary storage  device  such  as  hard disk   drives. This  data is  physically stored  in hard disk  in  two  states        (  for  magnetic  tapes it is south  and  north poles )  which  is represented  in the  binary form  in  a   computer system .

The OS performs number of file operations that includes creating new file , modifying the and deleting the files . The OS also presents the user friendy logical view of the files which includes folders and different types of files .    

Files For User
Logical Files View

A  computer system can be designed  to operate  in different modes in terms of number of  users working on the machine at the same time  , number of processors used, data handling  and  the number of applications running simultaneously  on  the  same  computer  system . 

A  computer system  also needs  to be configured accordingly and the system will  also need the  operating system which  can  support  such  operations . And therefore different types of operating system are used to support the different modes of  operation .

What Are Modes Of Operating Systems ?

Single User Single Tasking OS

A  computer system can be designed  to operate  in different modes in terms of number of  users working on the machine at the same time  , number of processors used, data handling  and  the number of applications running simultaneously  on  the  same  computer  system . 

A  computer system  also needs  to be configured accordingly and the system will  also need the  operating system which  can  support  such  operations . And therefore different types of operating system are used to support the different modes of  operation .

Types Of Operating System

The single user single tasking OS supports only single process being executed by single user using single processor . 

Whereas the single user multi tasking OS allows more than one program ( processes )  Or many instances of the same program to  run  concurrently. 

For example with MS Windows OS , the user can open multiple MS word document files at the same time .

The single user multi tasking OS  share common processing resources , such as a  CPU time   and   main  memory RAM .  In multi tasking process , only one CPU  is involved  but it switches from one program to another so quickly that it gives an illusion of executing all the programs  at  the same time.

Multi Processor Processing OS

The Multi Processor processing makes use of more than one processor in a single system to enhance the system performance . Due to more number of processors,  the  system performance is significantly improved  .  However , all the processors  share  the same  common  main  memory  (  RAM )  .

 A   computer system  with  multi  processor capability   needs  operating  system  which  can   support  multiple  programs   execution  simultaneously  being processed by number of processors . 

Multi Processor Processing
Real Time Processing Operating System

Real Time Operating System

A real-time operating system ( RTOS ) that is also commonly pronounced as “are-toss” is a multitasking operating system designed for real-time applications. A  real-time computing  guarantees  response  within  specific  time limits   and  thus  suitable  for  quick  reaction  systems  . 

The Such applications include embedded systems, industrial robots, scientific  research  equipment  and others. A  real-time computing  has extensive application especially in the field of military and space research .

The RTOS ensures a guaranteed  response  within  specific  time limits   and  thus  suitable  for  quick  reaction  systems. 

Common Operating Systems

Some of the most commonly used operating systems include :

Common Operating Systems

Microsoft Windows

Windows is Microsoft’s flagship operating system , the de facto standard for home and business computers .  Windows OS  is  GUI  based  operating system which  provides  a  very  user friendly  interface . Even  today  MS windows  has  a  leadership  position 

Google Android

Android is a mobile operating system developed by Google, based on the Linux kernel and designed   primarily  for  touch  screen   mobile devices  such  as  smart  phones and  tablets .

Apple iOS And Mac OS

The Apple iOS  and mac OS are  operating systems created and developed by Apple corporation  exclusively for its own hardware that includes iPhone , iPad , Apple Laptops and desktops .

The latest version of  iOS 12.3.1 And mac OS is 10.14.5 as on 2019 . Both iOS and mac OS are  considered to be the most advanced mobile and desktop operating system respectively. 

The Apple iOS  and mac OS are  also one of the most secured , powerful and user friendly OS with huge customer base across the world .


The Linux is a open source operating system. The  Linux OS, is a freely distributed, cross-platform operating system

The Linux is based on Unix that can be installed on PCs, laptops, notebooks, mobiles , tablet devices, video game consoles , even as a server OS , Supercomputers and other computing devices.


The first version of Unix was not open source but subsequently many derivatives of Unix were developed including some open source . Mac OS is also Unix derivatives .

The Unix is a stable and powerful  operating system that has been developed by many different vendors . There are many different derivatives of Unix systems that differ in terms of functionality , GUI  look  and feel , licensing terms and other non standard features , developed by these different  vendors.

Unix OS

Microsoft DOS

The advent of the IBM PC in 1981 was accompanied by the emergence of IBM PC-DOS, which was provided by Microsoft and later marketed virtually unchanged  as  Microsoft  MS-DOS.

The  DOS ( Disk Operating System ) was a  command-line operating system which borrowed many ideas from UNIX and other early operating systems, although it was essentially a single-user, single-tasking operating  system  without  any  GUI  support .

Operating System Architecture

Operating System Structure

The OS is a complex piece of system software which is designed to handle some of the most crucial and complex operations performed by the computer system . The OS provides an interface between the system user and the  computer hardware components .

The OS also allocate the required resources and the runtime environment to the application programs .The OS design is based on some structures which defines the internal architecture of the OS .

An operating system structure ( Also referred as OS Architecture )  is a term  that  specifies  the overall internal structure of the operating system.

It includes the logical components and the logical interrelationships of  various components and the functions of  these structural components  that  constitute  an  operating system

Computer System Architecture

Types Of Operating System Structures

Depending upon the internal structure , the Operating Systems can be grouped into of four major types as under :

OS Structure Types

Software Engineering , What is Software , SDLC

Simple Structure OS

As the name suggest , the simple structure OS has only four layers although it is not a layered OS . The MS DOS ( Disk Operating System )  was based on the simple structure . However , the simple structure OS had some major limitations .

In these OS , the application program had direct access to the BIOS drivers . If the application program fails due to some reason , which may cause system crash . The  Simple Structure OS  did not have a well defined structure  which made these OS vulnerable for system crash .

Simple Structure Operating Systems

Layered Structure OS

The lack of well defined layers and the modules was problem area for simple structure OS . To overcome these limitations,  the next generation of operating systems adopted a  layered Architecture approach of operating system developed in 1960’s.

In layered approach based OS , the operating system components are grouped in layers based on the functionality of these components . The bottom layer ( layer 0 ) is the hardware layer and the topmost layer ( layer n ).

In layered approach OS architecture , each top layer can use immediate bottom layer . And therefore , the functionality of the each layer needs to carefully designed and implemented in each layer .

Layered Structure OS
OS Architecture

In case of layered OS structure , the OS is divided into number of layers depending upon the functionality of layers .  It is relatively much easier to implement the layered architecture and that is the  main advantage .

On the other hand , the layered structure OS are relatively less efficient .The MS Windows NT which is a network OS and OS2 were based on the layered approach OS .

Monolithic Kernel Operating Systems

What Is Kernel In OS ?

The OS consist of number of components  and  the   core  software  components  of   an  operating system  are collectively called  as the  kernel . 

The kernel components include system software components that manages file system , Inter process communication , Input and output , Device Management and process Management . 

The kernel  has unrestricted access  and  also responsible to manage  all of the  resources  of  the  computer  system.

Monolithic Operating Systems Architecture

In  monolithic architecture operating systems , each layer of the operating system communicates only with the layer immediately placed above and  below  it . 

In this architecture , the lower-level  layers  provide  services to higher-level ones using an interface that hides  their  implementation.

Monolithic Kernel Architecture OS
Monolithic Kernel Architecture Operating Systems

And therefore , the Applications had access and  could communicate directly with any internal component of the operating system  which gave  unrestricted  system  access  . 

This  kind  of  layered  design  was perceived to  be  very   efficient  but  at the same time more vulnerable  for  system crash due to unrestricted  system  access.

Monolithic Kernel Operating Systems

What Is Micro-kernel In OS ?

In case of  micro-kernel architecture  , the kernel components includes only a very small number of  bare minimum essential services within  the kernel space in order to keep the kernel design  small and scaleable.

The services within the  micro-kernel area  typically include low-level memory management, inter-process communication and basic process synchronization  to enable processes to cooperate.

This  kind  of  micro-kernel  design  was observed to  be  more stable  and  at the same time less vulnerable  for  system crash caused due to unrestricted  system  access.

Micro Kernel Architecture OS
MicroKernel Architecture OS

In micro-kernel architecture design based operating systems , only critical components are placed inside kernel area .

And other  operating system components such as process management  and  device management are placed  outside  kernel area  which  execute outside  the  kernel  within  a  user area  with  lower  level of   system access.


Operating Systems Booting Process

The process of loading the main operating system into the RAM ( Random Access Memory ) is referred as booting process.

The operating system is essential system software which effectively handles some of the most important functions.

The system user can start using the computer only after the OS is fully loaded into the RAM. And therefore , the CPU initiates the booting process by activating another system software ( firmware ) called the BIOS.

The BIOS is a start up routine present on the motherboard in the form of BIOS chip. The BIOS main job is to search and load the operating system.

Operating System Booting Process , BIOS , How Computer Starts

What Is BIOS ?

Basic Input Output System

The BIOS  ( Basic Input Output System ) is a start up system program that gets activated every time the system is powered on . 

It is the BIOS that performs initial hardware check on some key components such as power supply unit ( PSU – SMPS ) , memory RAM , processor, display monitor  and keyboard. 

The BIOS  initiates the system booting process by starting a self diagnostic test called  POST. The POST stands for power on self test.

BIOS Chip On Motherboard

BIOS Chip On Motherboard

BIOS Start Up Screen

BIOS Start Up Screen

If the POST test is completed successfully , then the BIOS will proceed further and search for a capable operating system.

The BIOS loads the operating system into the main memory RAM and handover the control to the OS. The user can operate the system when OS is fully operational.

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What Is BIOS And How It Works ?

What Is CMOS ?

Complimentary Metal Oxide Semiconductor

During the computer system booting process the BIOS takes the hardware configuration data , settings from another source called CMOS memory.

The CMOS memory chip is a type of miniature volatile memory chip which stores the data required during the system booting process.

Since the CMOS is a type of volatile memory , it needs to be continuously powered so that it can retain this data. This power is provided by the CMOS battery.

CMOS Battery On Motherboard

CMOS Battery , BIOS

CMOS Battery

CMOS Battery on Motherboard , BIOS

Both BIOS and CMOS memory jointly participate into the system booting process to load the main operating system. 

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What Is CMOS And How It Works ?

What Is UEFI ?

Unified Extensible Firmware Interface

The UEFI is a new replacement for the firmware BIOS.  In simple words , the BIOS is a small piece of system software placed in a ROM chip on the motherboard. 

The UEFI is latest new advanced version of the BIOS that will be doing the same job previously done by the BIOS.  However , both BIOS and  UEFI operate differently.

What Is UEFI , UEFI Firmware

The UEFI has some major advantages as compared to the legacy BIOS. The UEFI offers a presentable GUI interface as compared to the text navigation menu of the BIOS.

The UEFI has also added number of security features and that has significantly improved the system security.

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What Is UEFI ?

Difference Between BIOS And UEFI

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