Operating system introduction to operating system

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

Introduction to Operating System
Introduction
What is a Computer?
Most important software – 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

Components of the Computer 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

Operating System : from user view
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

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

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

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

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

4. The Fourth Generation (1980 - present)
 Hardware : LSI (Large Scale Integration) Circuits
 Personal Computers evolved

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.

Memory Structure in Batch 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

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.

Multiprogramming with three programs

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.

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

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

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

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.

 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.

Operating system introduction to operating system

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Operating system introduction to operating system