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UNIT 1 CHAPTER 1 Introduction 1.0 Objectives 1.1 Introduction 1.2 What 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. Operating system allows multiple programs to be in memory and run at the same time. 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 19545 -55 Programming language Machine language Operating system Unheard Hardware Vacuum tubes, plugboard, Cables Computers ENIAC, Z3, Colossus 1.3.2 Second Generation OS-: 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 1955 -65 Programming language Fortran, assembler Operating system IBM’s operatinf system FM Hardware 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 allocates the CPU in turns to number of users Third generation computers were used for Large scientific calculations and massive commercial data-processing runs Year 1965-1980 Programming language Integrated Circuit Operating system Linux MINIX Hardware Integrated circuit Computers System/360. 1.3.4 Fourth Generation OS-: Fourth generation computers were also known as Personal computers Extremely small size computers could be created using microchips which made it possible for a single individual to have his own personal computer Companies like Intel and IBM started creating OS for their respective CPU User friendly GUI were built for general purpose usage Microsoft came up with different versions of Windows Network operating systems and distributed systems became popular in this era In network operating system, users log in to remote machines and copy files from one machine to another. A distributed operating system, is composed of multiple processors but appears to its users as a single uniprocessor unit Year 1980 – Present Programming language High level programming language Operating system DOS, Windows, UNIX, FreeBSD Hardware LSI(large Scale Integration) circuit, chips, transistors Computers IBM 4341, DEC 10,STAR 100 1.3.5 Fifth Generation OS Fifth generation was also known as Mobile computer, made by using Ultra Large Scale Integrated Chips New operating systems like symbians, Blackberry OS, iOS ,Android became popular in the market Devices become more portable and smaller in size Artificial intelligence is used on a large scale to construct a device which uses natural language processing for analysis of input. Computers in this era were capable of self learning Year 1990 – Present Programming language High level programming language Operating system iOS, Android, Symbians,RIM Hardware Ultra large scale integrated chip Computers Handheld devices, wearable devices, PDA, Smart phone 1.4 Computer Hardware 1.4.1 Processor CPU is the most vital part of the computer. The instructions are fetched from the memory and executed by CPU using fetch-decode-execute CPUs contains registers inside to hold key variables and temporary data. Special registers called as program counter contains memory address of the next instruction to be fetched. Program Status Word contains the condition code bits The Intel Pentium 4 introduced multithreading or hyperthreading to the x86 processor, allowing the CPU to hold the state of two different threads and then switch back and forth in nanosecond. A GPU is a processor with thousands of tiny cores which are very good for many small computations done in parallel like rendering polygons in graphics applications 1.4.2 Memory The basic expectations from the memory is its speed, storage and performance but a single memory is not capable of fulfilling the same The memory system is based on hierarchy of layers. Registers inside the CPU forms the top layer in the hierarchy which gives quick access to data. Cache memory is next in the hierarchy. Most heavily used data are kept inside the cache for high speed access using cache hit and cache miss. Two types of cache are present in the system depending upon the manufacturing company cache L1 and L2 The cache that is always inside the CPU is L1 which enters decoded instructions inside the CPU L2 cache holds megabytes of memory words which were recently used The difference between the L1 and L2 caches lies in the timing.
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