C o n f i d e n t i a l1

Course : BCA

Semester : III

Subject Code : BC 0042

Subject Name : Operating Systems

Unit number : 1

Unit Title : Overview of Operating System

Lecture Number : 1

Lecture Title : Overview of Operating System

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Unit-1 Overview of Operating System

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Overview of Operating system

Objectives

To understand

• definitions of program, process and thread

• definition of operating system

• what are the functions of operating system

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Unit-1 Overview of Operating System

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Topic covered

• Introduction to Operating systems

• What is operating system

• Functions of operating system

• Class Summary

Overview of Operating system

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Unit-1 Overview of Operating System

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Introduction to OS

What is program ?

Program is sequence of instructions which tells the computer what is the

task to be done.

Program can be written using high level or assembly languages.

The user normally uses a text editor to write their program in a high level

language, such as Pascal, C, Java, etc.

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Introduction to OS

What is language translators ?

A software used to translate a program written in any other computer

languages to machine language.

A compiler is used to translate a high level language program into

machine code.

A assembler is used to translate a assembly language program into

machine code.

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Introduction to OS

What is process ?

A process is a program in execution.

A process is executed sequentially, one instruction at a time.

A program is a passive entity. For example, a file on the disk.

A process on the other hand is an active entity.

A process being an active entity, changes state as execution roceeds.

A process can be any one of the following states:

New , Running, waiting, ready or terminated

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Introduction to OS

What is thread?

•Thread is a single sequence stream which allows a program to split itself

into two or more simultaneously running tasks.

•It is a basic unit of CPU utilization, and consists of a program counter, a

register set and a stack space.

•Because threads have some of the properties of processes, they are

sometimes called lightweight processes.

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What is OS ?

What is operating system?

•Operating System is a System Software(Set of system programs) which

provides an environment to help the user to execute the programs.

•The Operating System is a resource manager which allocates and

manages various resources like processor(s), main memory, input/output

devices and information on secondary storage devices.

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What is OS ?

•The purpose of an OS is to provide an environment in which a user can

execute programs in a convenient and efficient manner.

•The operating system must provide certain services to programs and to

the users of those programs in order to make the programming task

easier, these services will differ from one OS to another.

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Functions of operating system

Functions of Operating System

Operating systems perform the following important functions:

1. Processor management :

It means assigning processor to different tasks which has to be

performed by the computer system.

2. Memory management :

It means allocation of main memory and secondary storage areas to the

system programmes, as well as user programmes and data.

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Functions of operating system

3. Input and output management :

It means co-ordination and assignment of the different output and

input devices while one or more programmes are being

executed.

4. File system management :

Operating system is also responsible for maintenance of a file

system, in which the users are allowed to create, delete and

move files.

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Functions of operating system

5. Establishment and enforcement of a priority system :

It means the operating system determines and maintains the order in

which jobs are to be executed in the computer system.

6. Assignment of system resources, both software and hardware

to the various users of the system.

7. Provide a effective user interface

The user interacts with the operating systems through the user interface

and usually interested in the look and feel of the operating system

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Unit-1 Overview of Operating System

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Class Summary

•Introduction to Operating systems

•Concepts of program, process and thread

•What is operating system

•What are the Functions of operating system

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