Operating System

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UNIT 1 CHAPTER 1 Introduction 1 0 Objectives 1 1 Introduction 1 2 What is operating system 1 2 1 Definition 1 2 2 The Operating System as an Extended Machine 1 2 3 The Operating System as a Resource Manager 1 3 History of operating system 1 3 1 First Generation OS 1 3 2 Second Generation OS 1 3 3 Third Generation OS 1 3 4 Fourth Generation OS 1 3 5 Fifth Generation OS 1 4 Computer hardware 1 4 1 Processor 1 4 2 Memory 1 4 3 Disk 1 4 4 Booting of system 1 5 Let us Sum Up 1 6 List of Reference 1 7 Bibliography 1 8 Unit End Exercise 1 0 Objectives The objective of the chapter is as follow To get familiar with core component of operating systems To understand the different generation of operating system To understand the different functionality of system 1 1 Introduction Operating systems provides a clear best and simple view of the computer to the users Operating system performs the function of resource handling and distributing the resources to the different part of the system It is the intermediary between users and the computer system and provide a level of abstraction due to which complicated details can be kept hidden from the user 1 2 What is Operating System 1 2 1 Definition Operating System is a system software which acts as an intermediary between user and hardware Operating System keeps the complicated details of the hardware hidden from the user and provides user with easy and simple interface It performs functions which involves allocation of resources efficiently between user program file system Input Output device Figure 1 Abstract view of Operating system Reference Modern Operating system Fourth edition Andrew S Tanenbaum Herbert Bos Explanation of Figure 1 The hardware components lies at the bottom of the diagram It is considered as the most crucial part of computer system To protect the hardware from direct access it is kept at the lowest level of hierarchy Hardware components includes circuits input output device monitor etc Operating system runs in the kernel mode of the system wherein the OS gets an access to all hardware and can execute all machine instructions Other part of the system runs in user mode 1 2 2 The Operating System as an Extended Machine The structure of computers system at the machine language level is complicated to program especially for input output Programmers don t deal with hardware so a level of abstraction is supposed to be maintained Operating systems provides layer of abstraction for using disks files Abstraction allows a programs to create write and read files without having to deal with the messy details of how the hardware actually works Abstraction is the key to managing all the complexity Good abstractions turn a nearly impossible task into two manageable ones The first is defining and implementing the abstractions The second is using these abstractions to solve the problem at hand operating system primarily provides abstractions to application programs in a top down view Eg It is much easier to deal with photos emails songs and Web pages than with the details of these files on SATA or other disks 1 2 3 The Operating System as a Resource Manager Modern computers consist of processors memories timers disks mice network interfaces printers and a wide variety of other devices In the bottom up view the operating system provides for an orderly and controlled allocation of the processors memories and I O devices among the various programs time Operating system allows multiple programs to be in memory and run at the same Resource management includes multiplexing sharing resources in two different ways in time and in space In time multiplexed different programs takes turns using CPU First one of them gets to use the resource then the another and so on Eg Sharing the printer When multiple print jobs are queued up for printing on a single printer a decision has to be made about which one is to be printed next In space multiplexing Instead of the customers taking turns each one gets part of the resource Eg main memory is divided up among several running programs so each one can be resident at the same time 1 3 History of Operating system English mathematician Charles Babbage 1792 1871 developed the first true digital computer which was purely mechanical and the technology of his day could not produce 1 3 1 First Generation OS First generation were also known as Vacuum Tube Single group of people were responsible for creating building programming operating and maintenance of each machine Programming was done by connecting the electrical circuit on plugboard with thousands of cables Programmer used to sign up for a block of time using the signup sheet on the wall then come down to the machine room insert his or her plugboard into the computer and spend the next few hours hoping that none of the 20 000 or so vacuum tubes would burn out during the run Year Programming language Operating system Hardware Computers 1 3 2 Second Generation OS 19545 55 Machine language Unheard Vacuum tubes plugboard Cables ENIAC Z3 Colossus Second Generation computers were also known as Transistors and Batch Systems Computer in this era was reliable and manufactured for the purpose of selling it to the customers like government agencies or universities Separate groups were formed for working ono designing building and coding aspects of computer Computers were known as mainframes and were kept in separate rooms Separate machines were build for calculation and for input output Programs were known as job Jobs were entered in groups called as batch second generation computers were used for scientific and engineering calculations of physics and engineering Year Programming language Operating system Hardware 1955 65 Fortran assembler IBM s operatinf system FM Transistors and Batch Systems punch card magnetic tape Computers Mainframe IBM 1401 IBM 7094 1 3 3 Third Generation OS Third Generation computers were known ICs and Multiprogramming Maintaining two computers were not easy so IBM introduced its first computer names System 360 made by using Integrated circuit The main purpose of this generation was all software including the operating system OS 360 worked on all models Important feature identified in this generation was multiprogramming where in when one job was waiting for I O to complete another job could be using the CPU This way maximum utilization of CPU could be achieved Spooling that has an ability to read jobs from cards onto the disk Time sharing which


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