1. CHAPTER 1
Introduction
To
Operating System
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

2. Introduction to Operating System
Introduction
What is a Computer?
Most important software – Operating System
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

3. Introduction to Operating System
Operating System Concepts
Definition :
-> Manages the computer hardware and
-> Provides user program with simpler interface to the
hardware
 Goal :
-> Convenience for users; and
-> Efficient operation of the computer system
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

4. Introduction to Operating System
Components of the Computer System
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

5. Introduction to Operating System
Components of the Computer System
Hardware : physical devices –
processor, keyboard, mouse, monitor, etc.
Operating System : manages hardware and masks the
complex details of hardware from the user
 provides simple interface between application programs
and hardware
Application Programs : particular tasks, different kinds of
functionalities provided by OS
 airline reservation system, banking system
Users : interact with the system by using application
programs to perform particular tasks
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

6. Introduction to Operating System
Operating System : from user view
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic
A top down view
Considered as an extended machine
OS as a machine – easier to program
Hides all details from user. Provides a layer between user
and hardware
Need not to concern about the complexities of hardware
Simply uses the functionalities provided by the OS, such as
system calls, to make his job done
Goal : User Convenience

7. Introduction to Operating System
Operating System : from system view
A bottom-up view
Considered as a Resource Manager
OS manages all the resources such as CPU, memory, I/O
devices
Resources are shared in one of two ways :
(i) By multiplexing them in Time :
 Each user takes a turn to use the resource (CPU)
(ii) By multiplexing them in Space :
 Each user gets part of the resource (memory)
 Primary goal : Efficiency
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

8. Introduction to Operating System
History of Operating System
 Charles Babbage – a true digital computer
1. The First Generation (1945 - 1955)
 Hardware : vacuum tubes and plug boards
 Neumann and others succeeded in building Calculating
engine
 No OS, no programming languages
 Introduction of Punch Cards
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

9. Introduction to Operating System
History of Operating System
2. The Second Generation (1955 - 1965)
 Hardware : transistors
 Clear separation between
designers, builders, operators, programmers and maintenance
personnel
 Machines were called mainframes
 Batch Operating System took birth
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

10. Introduction to Operating System
History of Operating System
3. The Third Generation (1965 - 1980)
 Hardware : Integrated Circuits
 Multiprogramming OS and variations of it such as Time
sharing, Interactive, Multitasking OS came in picture
 SPOOLing (Simultaneous Peripheral Operation On Line)
began during this time duration
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

11. Introduction to Operating System
History of Operating System
4. The Fourth Generation (1980 - present)
 Hardware : LSI (Large Scale Integration) Circuits
 Personal Computers evolved
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

12. Introduction to Operating System
Types of Operating System
1. Batch Operating System
 input devices : card readers, tap drives
 output devices : line printers, punch cards, tap drives
 OS was very simple and resident in main memory
 Prepare a job and submit to operator. Job was consisted of
program, data and some control information
 sort them in batches with similar requirements, and as
computer became available, run them batch wise
 after some time (some hours or even after some days)
output appeared. Output includes result and error information.
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

13. Introduction to Operating System
Types of Operating System
Memory Structure in Batch Operating System
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

14. Introduction to Operating System
Types of Operating System
Disadvantages :
 Low throughput : CPU remains idle when I/O is going on
 Programmers do not have direct interaction with Job
 Debugging is possible only offline, after output appears
 Operations were too much time consuming
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

15. Introduction to Operating System
Types of Operating System
2. Multiprogramming Operating System
 Run more than one program concurrently
 more than one program loaded in main memory
simultaneously. These programs can be executed concurrently.
Memory is shared between OS and such kind of programs.
 Multiprogramming = Multitasking
 significantly improves system throughput and resource
utilization
 CPU can be utilized as much as possible. Eg. During I/O
operation, CPU will be free, and it can be allocated to other
Job.
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

16. Introduction to Operating System
Types of Operating System
Multiprogramming with three programs
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

17. Introduction to Operating System
Types of Operating System
Implementation :
1. Non-preemptive :
 A program is allowed to execute until it voluntarily gives up
the CPU
 A program voluntarily gives up the CPU when it waits for
some event, such as I/O operation, or when it terminates
 Once a CPU becomes free, it can be allocated to some other
program.
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

18. Introduction to Operating System
Types of Operating System
2. Preemptive :
 A program is allowed to execute for some maximum amount
of time.
 After this time, a CPU is forcibly taken away from the
program
 minimize the response time for user
 suitable for interactive programs
 Today most of the Operating Systems
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

19. Introduction to Operating System
Types of Operating System
Required Features :
 better memory management and protection
 swapping and virtual memory
 CPU scheduling
 Disk management and file system
 Synchronization & communication between running
programs and problems like deadlock should be overcome
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

20. Introduction to Operating System
Types of Operating System
3. Multi-user Operating System
 Single user Os allows single user to access computer system
at a time.
 Multiple users cannot use single computer at a time. Eg.
Situation at home
 Multi-user allow multiple users to access computer system
at a time
 remote access is provided via a network, So that users can
access the computer remotely using a terminal or other
computer
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

21. Introduction to Operating System
Types of Operating System
A terminal contains I/O devices eg. ATM machine or
computer at railway station
Multiple user can access the single computer through time-
sharing and multiprogramming
CPU is time-sliced at a regular interval
Eg. Unix, VMS and mainframe OS
The OS must make sure that –
 Each and every program executed by multiple users has
sufficient and separate resource
 Resources, such as printers, should be shared in fair and
proper way.
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic

22. Introduction to Operating System
Types of Operating System
 Request from one user should not affect the operation of
other users
 only authenticate and valid users should use the data stored
on computers
Expensive hardwares can be shared among several users
using multi-user OS. This provides better utilization of
resources.
As more users access it, the performance becomes slower and
slower.
Cost of hardware and software in multi-user environment is
more than single user OS.
Jaydeep Patel Dept. of Computer Engineering LJ Polytechnic