1.  CONTENTS:-
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2. INTRODUCTION
 An integrated set of programs that are used to manage
resources and operators
 A software that controls and monitors execution of all
programs including application program and other systems
software
 It is the interface between user and computer.

3. Structure of Operating System:
USERS
Other System Programs
Operating System
HARDWARE

4.  An operating system is a program that acts as an interface between the
user and the computer hardware and controls and manages the overall
resources of computer system.
 Goals of an OS:-
1. Making computer system convenient to use in effective manner.
2. Manages resources of a computer system.
Example of os:- Ms-dos
Windows
Macintosh
Unix

5. 1. Hardware – provides basic computing resources (CPU, memory, I/O
devices).
2. Operating system – controls and coordinates the use of the
hardware among the various application programs for the various
users.
3. Applications programs – define the ways in which the system
resources are used to solve the computing problems of the users
(compilers, database systems, video games, business programs).
4. Users (people, machines, other computers).

6. View of System Components

7. TYPES OF OS
 Early os or serial processing
 Batch os
 Multiprogrammed os
 Multitasking os
 Time sharing os
 Multiprocessing os
 Real time os
 Distributed os

8.  In serial operating system only one job resides in computer
memory and it remains there till it is executed. After
completion of job, next ob is entered.
 Disadvantages:- O.S
1. cpu remains idle for most of time.
2. Very slow
User
3. Waiting time of jobs are more Program
Area
 Advantages:-
1. Resource management is very easy.
2. allocation is very easy.

9.  It process a batch of jobs
 Does not allow user to interact computer directly.
 Each user prepares his job and submits to the operator.
 Major task is to transfer control automatically from one job to
next.
 Advantages:-
1. Faster than serial processing
2. Resource allocation and management is very easy.
 Disadvantages:-
1. Lack of interaction between user and job.
2. Turnaround time is high.
3. Off line debugging.

10.  It refers to holding more than one process in memory and
executing them concurrently.
 It increase cpu utilisation such that cpu always has one to execute.
 Example of multiprogramming is given below:-
Main memory
SUPERVISOR
Writing o/p data
PROGRAM A
PROGRAM B
PROGRAM C
(waiting for CPU)
CPU
Execution
Secondary disk storage
in progress

11.  Processor’s time is shared among multiple users
 Multiple users simultaneously access the system through
terminals.
 Advantages:-
1. Reduce CPU idle time.
2. Provides advantage of quick response.
 Disadvantages:-
1. Problem of data communication.
2. Question of security and integrity of user program and data
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12. Main memory
time sharing
Terminal 1 supervisor
User 1 User 1 User 1
Terminal 2
User 2 User 2
User 2
User n User n
Terminal n
User n Online
CPU storage

13. Multi processing or parallel
processing O.S
 This technique consist of two or more CPUs, perform more
than one job at a time.
Fig:-
CPU 1 Main memory CPU 2
I/O processor I/O processor
I/O units I/O units

14. 1. Better throughput
2. Better reliability
3. Saving cost

15. DISADVANTAGES
1. Large main memory is required
2. Such system are expensive.

16. Real time O.S
 It is a multiprogramming system that aims at executing real
time applications.
 Its main objective is their quick and predictable response to
events.
 Examples are:-
ATM machine
Flight control etc.
 Advantages:-
1. Better throughput
2. Response time is very less
 Disadvantages:-
1. Very costly
2. Large memory required

17. Distributed O.S
 A distributed system uses multiple central processors to serve
multiple real time applications.
 With distributed processing, related data at all terminals is
synchronized, updated simultaneously. It allows the user to
access remote resources in the same manner as local resources
as they do.
 It is a collection of processors that do not share memory. Each
processor has its own local memory.
 The use of multiple processors is invisible to the user i.e. the
users are not aware of where these file are residing. These are
handled automatically and efficiently by the os.