Computer Number system Note for IBPS PO

IBPS SO IT Officer Notes for Operating System

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IBPS SO IT Officer Notes for Operating System  

Operating system

An Operating System  is an interface between a computer user and computer hardware. An operating system is a software which performs all the basic tasks such as file management, memory management, process management and controlling peripheral devices such as disk drives and printers.

Some Operating Systems include Linux, Windows, OS X, VMS, OS/400, AIX, XP, etc.


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Following are functions of an operating System.

  • Memory Management
  • Process Management
  • Device Management
  • File Management
  • Security
  • Control over system performance
  • Job accounting
  • Error detecting aids
  • Coordination between other software and users

Memory Management

Memory management is the act of management computer Memory. Main memory provides a fast storage that can be accessed directly by the CPU. A program to be executed, must be reside in the main memory. An Operating System have the following activities for memory management −

  • Keeps tracks of primary memory,
  • In multi-programming, the OS decides which process will get memory when and how much.
  • Allocates the memory when a process requests it.
  • De-allocates the memory when a process no longer needs it.

Processor Management IBPS SO IT Officer Notes for Operating System

OS decides which process gets the processor for “how much time” and  “when”. This function is called process scheduling. An Operating System does the following activities for processor management −

  • Keeps tracks of processor and status of process known as traffic controller.
  • Allocates the  CPU to a process.
  • De-allocates processor when a process is no longer need it.

Device Management

An Operating System manages device communication through their respective drivers. Following activities for device management −

  • Keeps tracks of all devices known as I/O controller.
  • Decides which process gets the device when and for how much time.
  • Allocates the device in an efficient way.
  • De-allocates devices.

File Management

Used by OS to organise and keep tracking of files.

An Operating System does the following activities for file management −

  • Create and delete files.
  • East access to files.
  • Secure files.


Other Important Activities

Operating System performs some important activities −

  • Security − By use  of password and similar techniques, it prevents unauthorized access to programs and data.
  • Control over system performance − Records delays between request for a service and response from the system.
  • Job accounting − Keep  track of time and resources used by various jobs and users.
  • Error detecting  − detecting error by debugging and error detecting methods.
  • Coordination between other software and users − Coordination and assignment of compilers, interpreters, assemblers.

IBPS SO IT Officer Notes for Operating System

Types of operating system

Batch operating system

Batch operating system do not interact with the computer directly. User prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs are batched together and run as a group. The limitation of Batch Systems as follows −

  • Lack of interaction between user and the job.
  • CPU is idle because the speed of the I/O devices is slower than the CPU.
  • Difficult to provide the desired priority.

Time-sharing operating systems

Time-sharing is a technique which enables many people to use a specific computer system at the same time. Time-sharing or multitasking is a logical extension of multi-programming. Processor’s time which is shared among multiple users simultaneously is termed as time-sharing.

The operating system uses CPU scheduling and multi-programming to provide each user with a small portion of a time.

Advantages of Time-sharing operating systems are as follows −

  • Provides quick response.
  • Avoids duplication of software.
  • Reduces CPU idle time.

Disadvantages of Time-sharing operating systems

  • Reliability Problem.
  • Question of security and integrity of user programs and data.

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Distributed operating System

Means data can be stored and processed on multiple location. It manages a group of independent computers and makes them appear to be single computer.

The processors communicate with one another through various communication lines.These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function.

The advantages of distributed systems are as follows −

  • 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 is fails in  distributed system, then remaining sites can potentially continue operating.
  • Better service to the customers.
  • Reduction of the load on the host computer.
  • Reduction of delays in data processing.

Network operating System

A Network Operating System runs on a server and provides the ability to manage data, users, groups, security, applications, and other networking functions. The main 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 , a private network or to other networks.

Examples of network operating systems are Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD.

The advantages of network operating systems:

  • Centralized servers are highly stable.
  • Security is server managed.
  • Upgrades to new technologies and hardware could easily integrated into the system.
  • Remotely access to servers is possible from different locations and types of systems.

The disadvantages of network operating systems are as follows −

  • Expensive  of buying and running a server.
  • Dependency on a central location for most operations.
  • Regular maintenance and updates are required.

Real Time operating System

Real time OS is a multitasking is designed to an event with in a predetermined time. The time taken by the system to respond to an input and display of required updated information is termed as the response time. The response time is very less as compared to online processing.

For example, Scientific experiments, medical systems, industrial control systems, weapon systems, robots, air traffic control systems, etc.

Two types of real-time operating systems.

Hard real-time systems

Hard real-time systems ensure that critical tasks complete on time. In hard real-time systems, secondary storage is missing and the data is stored in ROM.

Soft real-time systems

Soft real-time systems are less restrictive. A critical real-time task gets priority over other tasks and retains in the priority until it completes. For example, multimedia, virtual reality etc


Multitasking is executed multiple task at a time. An OS does the following activities related to multitasking −

  • The user gives instructions to the operating system directly and receives an immediate response.
  • The OS handles multitasking that it can handle multiple operations and executes multiple programs at a time.
  • Multitasking OS are also known as Time-sharing systems.
  • These Operating Systems were developed to provide interactive use of a computer system at a reasonable price.
  • A time-shared operating system uses the concept of CPU scheduling..



when two or more programs reside in memory at the same time, is known as multi-programming. Multi-programming increases CPU utilization by organizing jobs so that the CPU always has one to execute.


Multi-programming activities related.

  • The operating system keeps multiple jobs in memory at a time.
  • set of jobs is a subset of the jobs kept in the job pool.
  • The operating system picks and begins to execute one of the jobs in the memory.



  • High and efficient CPU utilization.
  • User feels that many programs are allotted CPU almost simultaneously.


  • CPU scheduling is required.
  • To accommodate many jobs in memory, memory management is required.


Spooling means to putting data of various I/O jobs in a buffer. This buffer is a special area in memory or hard disk which is accessible to I/O devices.

following activities related to distributed environment −

  • Handling I/O device data spooling as devices have different data access rates.
  • Maintains the spooling buffer which provides a waiting station where data can rest while the slower device catches up.
  • Deal-locates the devices.



  • The spooling operation uses a disk as a very large buffer.
  • Spooling is capable of overlapping I/O operation for one job with processor operations for another job.

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Process Life Cycle

process execution passes through different states. These stages may differ in different operating systems.

New : the process is being created.

Running : instructions are being executed.

Waiting : process is waiting for an event to occur.

Ready : process is waiting for a processor.

Terminated : process has finished execution.

Process Control Block (PCB)

A Process Control Block represented in the Operating System for every process. The PCB is identified by an integer process ID (PID). PCB contains information that makes the process an active entity.

Information associated with each process:

1 ) Process state : process states are New, ready, running,waiting,terminated.

2) Program counter: indicate the next instruction to be executed.

3) CU registers : Where process need to be storage after execution.

4) CPU scheduling information : Includes information such as process priority, pointer to scheduling queue.

5) Memory management information :  Contains value of  base registers and limit registers, page tables, segment tables.

6) Accounting information : includes amount of processors tine and real time used, time limits, account numbers etc.

7) I/O status information : Includes list of I/O devices allocates to the process, list of open files.


Process scheduling

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