Railways Computers Science Operating System Operating System

Operating System

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Operating System


An operating system consists of a set of programs, which controls, coordinates and supervises the activities of the various components of a computer system. It is a program which acts as an interface between the user and the hardware. The interface enables a user to utilise hardware resources very efficiently. Operating system (OS) is an organised collection or intergrated set of specialised programs that controls the overall operations of a computer. It is a program that must be on any computer for proper booting.


Functions of Operating System

Operating system is a large and complex software consisting of several components. It is responsible for managing all the resources attached to a computer system.

Following functions are provided by an operating system to the convenience of users


Process Management

‘A Process is a program under execution'. It is the task which is currently being executed by the processor (CPU). The operating system handles the creation and deletion of processes and also manages the scheduling and synchronisation of process. Process management is the important part of an operating system which enables the activities of planning, monitoring and performance of a process.


Memory Management

Memory management of an operating system takes care of allocation and de-allocation of main memory to various processes. Managing the primary memory, sharing and minimising memory access time are the basic goals of the memory management. It also keeps track of memory usage. The performance of memory management is crucial for the performance of entire system.


File Management

File management module of operating system manages files held on various storage devices as well as transfers file from one storage device to another. The file management includes creating and deleting both files and directories, allocating space for files, keeping back-up, securing, easy access to files.


Input/Output Management

The Input/Output management module of the OS coordinates and assigns different input and output devices, namely terminals, printers, disk drives, tape drives, etc. Input/Output Management controls all I/O devices, keeps track of I/O requests, issues commands to these devices and takes measures which would ensure that data is transmitted efficiently and correctly to and from I/O devices.


Types of Operating System

The operating systems are classified as


Batch Processing Operating System

In batch processing operating system, a number of jobs are put together and executed as a group. This operating system is responsible for scheduling the jobs according to priority and the resource required. It is the type of OS which does not interact with the computer directly, e.g. Unix.


Single User Operating System

It is a type of operating system which allows only one user at a time. Operating system for personal computer (PC) is single user OS. They are designed to manage one task at a time. e.g. MS-DOS, Windows 9X.



Multi User Operating System

This OS allows multiple users to access a computer system concurrently. It is used in computer networks that allows same data and applications to be accessed by multiple users at the same time. e.g. VMS, etc.


Multi-Tasking Operating System

In multi-tasking operating system, more than one processes can be executed concurrently. It also allows the user to switch between the running applications. e.g. Linux, Unix, Windows 95.

Multi-tasking OS can be classified as follow

(a) Preemptive Multi-tasking OS It is a type of multi-tasking that allows computer programs to share operating system and underlying harware resources. It divides its overall operating, computing time between processes, and the switching of resources between different processes occurs through predefined criteria, e.g. OS/2, Window 95/NT, etc.

(b) Cooperative Multi-Tasking OS It is the simplest form of multi-tasking. In it, each program can control the CPU for as long as it need it. If a program is not using the CPU, however it can allow another program to use it temporarily, e.g. Mac OS, MS-Windows 3-X, etc


Time Sharing Operating System

In time sharing OS, a small amount of time is allocated for the processing simultanously. The time sharing operating system allows multiple programs to simultaneously share the computer resources. It provides to each process to be run on. e.g. Mac OS,


Real Time Operating Sytem (RTOS)

The main objective of real time operating systems is their quick and predictable response to events than any other operating system. Real time operating systems are designed to respond to an event within a predetermined time. It must have preemptive kernels to execute a program. They are often used in applications such as flight reservation system, military applications, etc. These types of operating system increase the availability and reliability of the system, e.g. Lynx OS, etc.

There are two types of real time operating system

(a) Hard Real Time OS It is referred to as an operating system that can absolutely guarantee a maximum time for the operations, it performs.

(b) Soft Real Time OS It is referred to as an operating system that cannot absolutely guarantee a maximum time for the operations, it performs.


User Interface

An operating system provides an interface between the computer user and the hardware. The user interface is one of the most important parts of any operating system because it allows users to easily access and communicate with the applications and the hardware.

The user can interact with the computer by using mainly two kinds of interfaces


Graphical User Interface (GUI)

It is a computer program that enables a person to communicate with a computer through the use of symbols, visual metaphors and pointing devices. It is best known for its implementation in Apple products.

The first graphical user interface was designed by Xerox Corporation in 1970s. GUIs can be found in hand held devices such as MP3 players, portable media players, gaming devices, etc.


Character User Interface (CUD

It is also known as Command Line Interface (CLI). CUI is a mechanism of interacting with a computer system or software by typing commands to perform specific tasks. Programs with character user interface are generally easier to automate via scripting. CUI only uses text types one after another just as commands used in MS-DOS.



It is a boot strapping process which starts the operating system when a computer is switched ON and the operating system gets loaded from hard disk to main memory. There are two types of booting

·      Cold Booting When a computer is turned ON after it has been completely shut down. 

·      Warm Booting When a computer is restarted by pressing the combination of Ctrl + Alt + Del Keys or by restarted button,         



Some Important Operating System

Some popular operating systems are as follows

  1. UNIX The first version of Unix was developed in 1969 by Ken-Thompson and Dennis Ritchie at AT & T Bell Laboratories. It is primarily used to a server rather than a workstation and should not be used by anyone who does not understand the system.
  2. Apple Macintosh (Mac OS) It was introduced in January, 1984 by Steve Jobs and was initially named as system software, which was later renamed as Mac OS. Most recent version of OS is based on Unix because it has a good graphical interface.
  3. LINUX The first Linux Kernel was released in October, 1991 by Linus. It is an open source software, means anyone can download it and use it without any fees. Linux is similar to Unix in operations. It is difficult to understand by anyone who does not understand the system and can be difficult to learn.
  4. SOLARIS It is a free UNIX based OS

developed by Sun Microsystems. The first version of Sun Microsystems was published in 1992 and coined as SunOS.

  1. BOSS (Bharat Operating System Solutions) BOSS GNU/Linux (or simply BOSS) developed by C-DAC (Centre for Development of Advanced Computing) was initially released in 2007 and derived from Debian for enhancing the use of Free/Open Source Software throughout India. BOSS Linux provides GUI to the user.      
  2. Microsoft Windows It is an operating system, based on GUI, developed by Microsoft. Microsoft first introduced an operating environment named Windows in November 1985 in response to the growing interest in GUIs.                                


Mobile Operating System

This OS operates on Smartphones, Tablets and Digital Mobile devices. It controls mobile devices and its design supports wireless communication and different types of mobile applications. It has built-in support for mobile multimedia formats

Some popular mobile operating systems are as follows

(i) Android It is a mobile OS developed by Google, which is based on Linux Kernel. It is basically designed for touch screen mobile devices like Tablets, Smartphones, etc. Now-a-days, it is most common as used in mobile phones. The latest version of Android is Nougat which was released on 22 August, 2016.

(ii) Symbian It is the OS developed and sold by Symbian Ltd. It is an open source mobile OS designed for Smartphones. It has been used by many major handset manufacturers including Motorola, Nokia, Samsung, Sony, etc. The latest version of Symbian is Nokia Belle which was released in October 2012.

(iii) IOS It is the popular mobile operating system developed by Apple Incorporation. This operating system is commonly used in Apple iPhone, iPod Touch, iPad, etc. The latest version of iOS is iOS 10.0.2 which was released on 23th September 2016

(iv) BlackBerry it is the most secure operating system used in leading Smartphones developed by BlackBerry Company. It also supports WAP 1.2. The latest version of Blackberry is BlackBerry OS 10.3.3 which was released in 2016.


MS-DOS (Microsoft - Disk Operating System)

The DOS OS was developed by Microsoft in 1980 for microcomputers. MS-DOS was the first operating system that run on PC developed by IBM Corporation in 1981. DOS is a single user Operating system. It is only operating system, which can be loaded in the main memory of the computer using a single disk.


Structure of DOS

There are four essential programs associated with the control of computer and the way it interacts with them.

(a) The Boot Record It includes loading the operating system into main memory. It is the main program of MS-DOS.

(b) The Basic Input/Output System (BIOS. sys) it provides an interface between the hardware and programs.

(c) The MSDOS. Sys Program It is a collection of program routines and data tables that provides high level programs such as application programs.

(d) The Command.com Program it provides a standard set of commands that gives users access to file management, configuration and miscellaneous functions.


Configuration of DOS

Config. Sys, Autoexec, bat provide the environment to computer to set commands.

(a) CONFIG.sys It adjusts the system according to commands.

(b) Auto Exec.bat when the system is powered on, this file executes in automatically command line.


Important Extensions and their Meaning





Executable files


Command files


Batch files


Document files


Text files


Program files


Over lays


System files


Types of DOS Commands

There are two kinds of DOS command, Internal and External.

(a) Internal Commands These commands are automatically loaded into main memory when the booting process gets completed, e.g. DATE, TIME, VER, VOL, DIR, COPY, etc.

(b) External Commands These commands require external files to be loaded in the computer to run. e.g. Checking disk, comparing disk, formatting, etc.


Important Commands and their Uses





Call one batch program from another


Change Directory-move to a specific folder


Clear the screen


Check the hard drive running position


Copy one or more files to another location


Display or set the date


Delete one or more files


Display a list of files and folders


Delete one or more files


View and edit files


Quit the current script/routine and set an error level


To erase and prepare and disk drive


Conditionally perform a command


Create new folders


Move files from one folder to another


Display or set a search path for executable files


Prints data to a printer port


Change the command prompt


Rename a file or directory


Remove an empty directory


Sort the input and displays the output to the screen


Start a program, command or batch file


Display or set the system time


Display the contents of a text file


Display version information f


Copy multiple files, directories, or drives ; from one location to another



  • Spooling is the process of sending data to a spool (or buffers or temporary storage area) of the computer's memory.
  • Kernel is the core of the operating system that supports the process by providing a path to the peripheral devices.         
  • Shell is the program which interprets commands given by the user.
  • Thread is a task that runs with other tasks concurrently within the same process. Virtual memory is a space on hard disk which is used by CPU as extended RAM.

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