Operating System Notes

 Unit – 1 

Introduction 

. An Operating System is the Set of instructions which is provide the conventional way between the         Hardware and Software.

Architecture of Operating System –

Functions Of Operating System –

  There are Various Type of Functions of Operating System

1. Memory Management

 2. Processor Management 

3. Device Management 

4. File Management 

5. Security 

6. Control over system performance 

7. Job accounting 

8. Error detecting aids 

9. Coordination between other software and users

Memory Management –

Memory management refers to management of Primary Memory or Main Memory. Main memory is a large array of words or bytes where each word or byte has its own address. 

Main memory provides a fast storage that can be accessed directly by the CPU. For a program to be executed, it must in the main memory. An Operating System does the following activities for memory management.

 Keeps tracks of primary memory, i.e., what part of it are in use by whom, what part are not in use.  In multiprogramming, the OS decides which process will get memory when and how much.  Allocates the memory when a process requests it to do so.  De-allocates the memory when a process no longer needs it or has been terminated.

Processor Management -

In multiprogramming environment, the OS decides which process gets the processor when and for how much time. This function is called process scheduling. An Operating System does the following activities for processor management –

 Keeps tracks of processor and status of process. The program responsible for this task is known as traffic controller.  Allocates the processor (CPU) to a process.  De-allocates processor when a process is no longer required

Device Management -

An Operating System manages device communication via their respective drivers. It does the following activities for device management –

 Keeps tracks of all devices. Program responsible for this task is known as the I/O controller.     Decides which process gets the device when and for how much time

 Allocates the device in the efficient way. 

 De-allocates devices.

Security Management –By means of password and similar other techniques, it prevents unauthorized access to programs and data. 

Control over system performance − Recording delays between request for a service and response from the system. 

Job accounting − Keeping track of time and resources used by various jobs and users. 

Error detecting aids − Production of dumps, traces, error messages, and other debugging and error detecting aids. 

Coordination between other software and users − Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems.