Operating System

Long Answer questions

Question: What is OS? Explain the main functions of OS. [10 marks]

Ans: An operating system, OS, is the master program that manages all the hardware and software resources of the computer. It makes the hardware operable and provides an interface to the user to use the computer. Windows, Mac OS, IOS etc are the examples of OS.

Following are the main functions of OS:

1.  Process Management
2.  Memory management
3.  I/O management
4.  Device management
5.  File management
6.  Virtual memory management
7.  Interrupt handling
8.  Dead lock prevention
9.  Providing Security
10.  Providing user interface
11.  Command Interpreter
12.  Time sharing

1) Process management

Process management refers to the managing of CPU and its processing task. OS is responsible for managing the processing task so that the entire programs used by the user are efficiently and effectively processed by the CPU. OS uses scheduling and time sharing to manage process.

2) Memory Management

OS is responsible for controlling and managing all the operations of memory. OS allocates the required memory space and stores data on that memory space.

3) I/O Management

I/O refers to input and output. All the inputs and outputs are controlled and managed by OS. It instructs input unit to accept data, process it and provide the result to output unit after processing.

4) Device Management

OS is responsible for managing and controlling all the devices of the computer system. These devices include I/O, CPU, memory and other components. OS allocates the CPU time for processing and using these devices.

5) File Management

A file is a collection of data. OS is responsible for all the file related operations including creating a new file, storing data in a file, reading a file, copy/cut, paste operation the file, renaming of a file, deleting a file etc.

6) Virtual Memory Management

In a multi programming environment when multiple programs are used at a same time, the space of primary memory (RAM) may not be enough for storing all the programs. In this case, OS uses free space of secondary memory like Hard disk) to store the contents of RAM. This free space of secondary memory used by OS is called virtual memory. OS is responsible for creating and managing the virtual memory. Modern OS can increase or decrease the size of virtual memory as per need.

7) Interrupt Handling

An interrupt is a signal generated by hardware or software component when they require attention of the CPU. Interrupt are always given high priority by OS. When an interrupt occurs, the processing task of CPU is stopped, the interrupt is executed and the previous task of CPU is continued.

8) Dead lock Prevention

A dead lock is a situation in which neither the processing task of CPU is completed nor the CPU is released to execute other task. In this case CPU remains in the idle state. OS is responsible for preventing from the dead lock. However if the dead lock occurs, OS detects dead lock and recover from the dead lock.

9) Providing Security

OS provides high security on the resources of the computer so that it can be used only by the permitted users. OS provides two types of security:

•  Authentication
•  Access Control

10) Providing User Interface

User interface is the layer through which the user uses the computer. OS provides to types of user interfaces:

•  GUI (Graphical User Interface)
•  CUI ( Command/Character User Interface)

11) Command Interpreter

OS is responsible for reading the commands from the user, identify the task to be done and perform that task. The command can be either text or graphical command.

12) Time Sharing
Time sharing is the process of dividing the CPU time in small units and executing multiple task one after another. It is used in multi tasking, multi programming or multi user system. It is required when the number of processing task is more than the number of processor.