INTRODUCTION TO OPERATING SYSTEM - WordPress

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CHAPTER-1:INTRODUCTION TOOPERATING SYSTEM:

TOPICS TO BE COVERED 1.1 Need of Operating System1.2 Evolution of os1.3 operating systemi.Batchii.Multiprogrammingiii. Time sharingiv. Real timev.Multitaskingvi. Multithreding1.4 operating system servicies1.5 case studyi.Linuxii.Windows 7

NEED OF OPERATING SYSTEMThe need for operating system arises from thatuser need services and OS provides that services. The central part of a computer system is aprocessing engine called CPU.A system shouldmake it possible for a user’s application to usethat processing unit. Auser application would need to storeinformation. The OS makes memory available toan application when required. Similarly user programs use input facility tocommunicate with the application using keyboard or mouse.

The output is usually provided by a video monitoror printer.OS provides following resources for manyapplication (like document design ,Accounting ,Email ,Image processing ,Games)1.Processing information2.Storage information3.Mechanism to input information4.Provision for outputting information

CONCEPT OF OPERATING SYSTEMDefine Operating system? The operating system controls and coordinates theuser of the hardware among the various applicationprograms for the various users. It hides complexity of its hardware from user andprovide easy interface.An Operating system acts as government; it providesan environment within which other programs can douseful work.

Operating system acts as a resource allocator. Acomputer system has many resources like CPU time,memory space, file storage space, I/O devices etc. The operating system acts as manager of theseresources and allocates them to specific programs andusers as necessary for tasks efficiently. An operating system is a control program. It controlsthe execution of user programs to prevent errors andimproper use of the computer. ThePrimary goal of operating system isconvenience for the user. The operating systemmakes the use of system easier. The secondary goal of operating system is efficientoperation of the computer system.

COMPONENTS OF COMPUTER SYSTEM A Computer system can be divided into fourcomponents:1.2.3.4.HardwareOperating SystemApplication ProgramsUsers

Hardware :The hardware of computer systemincludes the Central Processing Unit (CPU), thememory, and the input/output (I/O) devices. Theyare the basic resources. application program includes compilers, databasesystem, games, and business programs. They definethe way in which the hardware resources are to beused to solve the computing problems of the users. Users :There are many different users trying to solvedifferent problems using different applicationprograms. Operating system :The operating system controlsand coordinates the user of the hardware among thevarious application programs for the various users.

EVOLUTION OF OS Serial ProcessingUsers access the computer in series. From thelate 1940's to mid 1950's, the programmerinteracted directly with computer hardware i.e.,no operating system. These machines were runwith a console consisting of display lights, toggleswitches, some form of input device and a printer.Programs in machine code are loaded with theinput device like card reader. If an error occurthe program was halted and the error conditionwas indicated by lights. Programmers examinethe registers and main memory to determineerror. If the program is success, then output willappear on the printer.

Simple Batch SystemsTo speed up processing, jobs with similar needsare batched together and run as a group. Thus,the programmers will leave their programs withthe operator. The operator will sort programsinto batches with similar requirements.The problems with Batch Systems are:Lack of interaction between the user and job. CPU is often idle, because the speeds of themechanical I/O devices are slower than CPU.

Personal-Computer Systems (PCs)A computer system is dedicated to a single user iscalled personal computer, appeared in the 1970s.Micro computers are considerably smaller andless expensive than mainframe computers. Thegoals of the operating system have changed withtime; instead of maximizing CPU and peripheralutilization, the systems developed for maximizinguser convenience and responsiveness.For e.g., MS-DOS, Microsoft Windows and AppleMacintosh.

Parallel SystemsMost systems to date are single-processorsystems; that is they have only one main CPU.Multiprocessor systems have more than oneprocessor.The advantages of parallel system are as follows:throughput (Number of jobs to finish in a timeperiod) Save money by sharing peripherals, cabinets andpower supplies Increase reliability Fault-tolerant (Failure of one processor will nothalt the system).

TYPES OF OSI. BATCH OS Early computers were large machines having inputdevices like card readers and tape drives and outputdevices like line printers, tape drives and cardpunches. The users of such system did not interactdirectly with the computer system, the userprepare job consisting of – data, program and controlinformation about the job and use to submit it tocomputer operator. The operating system fairly simple its major taskwas to transfer control automatically from onejob to next. The operating system was always inmemory.

Operators used to batch up jobs with similarneeds into a group to speed up the processing.The operators use to batch up the jobs submittedto him. The batch system has no interaction betweenthe user and the job while the job isexecuting. The job is prepared and submitted, and sometime later the output appears. The delay betweenjob submission and job completion is calledturnaround time. The CPU is often idle. This idleness occursbecause the speed of the mechanical I/O devicesis slower than electronic devices.

OperatingsystemInput(batch of jobs)Userprogram AreaOutput

Advantage: Simple Difficult to debug program. A job could enter an infinite loop. Due to lack of protection scheme, one batch job canaffect pending jobs.Disadvantage: Low throughput, CPU remains idle when I/O is goingon Debugging is possible only offline, after output appears Operation were too much time consuming Programmers do not have direct interaction with job.

II. MULTIPROGRAMMING OPERATING SYSTEM:Multiprogramming increases CPU utilization byorganizing jobs so that the CPU always has one job toexecute.Operatingsystemjob1job2job3job4

The operating system keeps several jobs in memorysimultaneously.This set of jobs is a subset of the jobs kept in the jobpool the number of jobs that can be keptsimultaneously in memory is usually much smallerthan the number of jobs that can be in the job pool.Operating system picks and begins to execute one ofthe jobs in memory and the other job may have towait for some task, such as I/O operation.In multiprogramming system, the CPU simplyswitches to, and executes another job. When thatjob needs to wait, the CPU is switched to anotherjob.

Eventually the first job finishes waiting and getsCPU back .CPU has always at least one job toexecute.In multiprogramming operating system all the jobsthat enter the system are kept in the pool. Thispool consists of all processes residing on diskawaiting allocation of main memory.When the operating system selects a job pool, itloads that job into main memory is called jobscheduling.If several jobs are ready to run at the same time,the system must choose among them, this decisionis called CPU scheduling.

ADVANTAGE High and efficient CPU utilization. User feels that many programs are allotted CPUalmost simultaneously.DISADVANTAGECPU scheduling is required. To accommodate many jobs in memory, memorymanagement is required.

IV.REAL TIME OPERATINGSYSTEMA real-time operating system is used where thereare rigid time requirement on the operation of aprocessor or the flow of data, and thus is oftenused as a control device in a dedicated application.RTOS has very little user-interface ,capability andno end user utilities. RTOS always controls inputs and respond withindefined time constraint. Systems that control scientific experiments,medical imaging systems, industrial controlsystems, and some displays, automobile-enginefuel-injection system are real-time system.

A real-time operating system has well-defined, fixedtime constraints processing must be done with thedefined constraints, or the system will fail.There are two flavours of real-time systems:1. Hard real time2. soft real time

Hard real-time: A hard real-time system guarantees that critical taskscomplete on time. This goal requires that all delays in the system bebounded , from the retrieval of stored data to the timethat takes the operating system to finish any requestmade of it.Secondary storage of any sort is usually limited ormissing , with data being stored in short-term memoryor in read-only memory(ROM).Most advanced operating system features such asvirtual memory is not found in real-time system. Ex: oil refinery (plant),ATM

Soft real-time system: A less restrictive type of real-time operating system isa soft real-time system, where a critical real-time taskgets priority over other tasks , and retains that priorityuntil it completes. Soft real-time system have more limited utility thathard real-time system.They are risky if used for industrial control androbotics because of their lack of deadline support. They are useful in multimedia , virtual reality, andadvanced scientific projects such as underseaexploration and planetary rovers. Ex: digital audio ,multimedia

V. MULTITASKING OPERATING SYSTEMTIME – SHARING O.S.:ORIt is a logical extension of multiprogrammingoperating system. The ability to execute more than one task at thesame time, a task being a program is calledmultitasking. The terms multitasking and multiprocessing areoften used interchangeably although multiprocessingimplies that more than one CPU is involved. In multitasking, only one CPU is involved, but itswitches from one program to another so quickly thateach user may interact with each program while it isrunning. So it gives the appearance of executing allof the programs at the same time.

A time – shared operating system uses CPUscheduling and multiprogramming to provides eachuser with a small portion of a time – shared computer.Each user has at least one separate program inmemory.A program in execution is called processTime slice is amount of that is given to process toexecute on processor (CPU).A time – Sharing operating system must have tection file system and disk management.

There are two basic types of multitasking:1.Pre-emptive multitasking (forcibly)2.Non pre-emptive or cooperative multitaskingvoluntarily) (Preemptive - a program is allowed to execute onlyfor some maximum time duration, after this timeduration CPU is forcibly taken away from theprogram.Minimize the response five for user.Ex: OS/2, Windows 95, Windows NT, the Amigaoperating system and UNIX use

Non pre emptiveNon pre-emptive multitasking, each programcan control the CPU for as long as it needs it. If a program is not using the CPU .However, itcan allow another program to use it temporarily. Ex: Microsoft Windows 3.x and the MultiFinder(for Macintosh computers)

VI.MULTITHREADING OPERATING SYSTEMThread is a flow of control within a process. A thread also called a lightweight process (L W P)is a basic unit of CPU utilization. Thread contains a thread ID, a program counter, aregister set, and a stack.It shares data with other threads belong to the sameprocess like its code section, data section and otheroperating system resources.Process is a heavy eight process, has a singlethread of control.

If the process has multiple threads of control, it cando more than one task at a time.For ex: A web browser might have one threaddisplay images or text while another threadretrieves data from the network.A word process may have a thread for displayinggraphics, another thread for reading keystrokefrom users, and a third thread for performingspelling and grammar checking.

Advantage of multithread programming Responsiveness:Multithreading an interactive application may allowa program to continue running even if part of it isblocked or is performing lengthy operation, soincreasing responsiveness to the user.Resource sharingThreads share the memory and resources of theprocess to which they belong.

3. Economy Allocating memory and resources for process creationis costly. Threads share resources of the process towhich they belong, it is more economical to createand context switch threads.4. Utilization of multiprocessor architecture Multithreadingcan be greatly increased inmultiprocessor architectures, whereeach threadmay be running in parallel on a multiprocessor. A single-threaded process can only run on one CPU,no matter how many are available. Multithreadingon a multi-CPU machine increases concurrency.

OPERATING SYSTEM SERVICESORFUNCTION OF OPERATING SYSTEM The operating system provides an environmentfor the execution of programs.The operating system provides services toprograms to the users of those programs .Theoperating system services are provided for theconvenience of the programmer.

FOR USER:Operating system provides services to the userprogram and system.1) User Interface: it provides interface to user souser can perform some action. It provides threetypes of interfaces, Command line Interface (CLI), in which usercan type command and methods for executingthem. Batch interface, in which commands anddirectives to control those commands are enteredinto files ,and those files are executed. Graphical User Interface (GUI),in whichinterface is a window system with pointing deviceto direct I/O ,chooses from menus, keyboard toenter text.

2) Program execution: The system must be able toload a program into memory and run it. Theprogram must be able to end its execution eithernormally or abnormally (indicating error).3) I/O operations: A running program mayI/O involves a file or an I/O device. Fordevices, special functions may be desired.For efficiency protection , users usuallycontrol I/O devices directly. The operatingprovides a means to do I/O.requirespecificcannotsystem4) File-system manipulation: The programs need toread and write files and programs must also createand delete files. The operating system maintains thefile system.

5) Communications: In many conditions the processneeds to exchange information with another process.Such communications can occur in two ways: The fist takes place between processes that areexecuting on the same computer.The second takes place between processes that areexecuting on different computer systems that are tiedtogether by a network.Communications may be implemented via sharedmemory or via message passing , in which theinformation is moved between processes by operatingsystem.

6. Error Detection: The operating system constantlyneeds to be aware of possible errors. Errors mayoccur in the CPU and memory hardware, in I/Odevices and in user programs. For each type of errors, the operating system shouldtake the proper action to ensure correct andconsistent computing.

FOR SYSTEM Operating a system function that exists not forhelping the user, but rather ensuring the efficientoperation of the system.7) Resource allocation: Operating system managesmany resources like CPU cycles, main memory, andfile storage. Resources are allocated to multipleusers. Some resourceshave special allocation code,whereas others may have general request andrelease code. For eg. In determining how best to use the CPU,the operating system have CPU- scheduling routinesthat takes account the speed of the CPU,the jobsthat must be executed, the number of registers.

8) Accounting: The tracking of which user use howmany and which kind of computer resources can beused for billing or simply accumulating usagestatistics. Usage statistics may be a valuable tool forresearchers who wish to reconfigure the system toimprove computing services.9)Protection: Protection involves ensuring that all access tosystem resources is controlled.

THE USER VIEW AND OPERATING VIEW Operating system can be explored from two viewpoints: the user view and system view.User View The user view of the computer varies by theinterface being used. It is top down view Primary goal :user convenience

1. Single user systemPc consisting of monitor, keyboard, mouse, andsystem unit are designed to be used by singleperson.(system that is used by single person is asingle user system).In the case, the operating system is designed mostlyfor case of use, with some attention paid onperformance, and none paid to resource utilization.Performance is important to the user, but it does notmatter if the most of the system is sitting idle ,waiting for the slow I/O speed of the user.

2) User connected to Mainframe or MinicomputerMany user are connected to mainframe orminicomputer through terminal to access to share theresources and exchange information. From that user’s point of view, the operating system isdesigned to maximize resource utilization. 3) User on Workstations User at workstation, connected to networks of otherworkstations and servers have dedicated resources attheir disposal , but they also share the resource such asnetworking and server – file , compute and printservers. The operating system is designed to compromisebetween individual usability and resource utilization.

5)Handheld computers These devices are mostly standalone, used singly byindividual users. Some are connected to network,either directly by wire or through wireless modems. Due to power and interface limitations they performrelatively few remote operations.The operating system are designed mostly forindividual usability (but performance per amount ofbattery life is important.6) Embedded Computers Some computers have little or no user view for egembedded computers.

System view It is bottom up view.From computer‘s view the operating system is theprogram that is most intimate with hardware.The operating system is a resource allocator. Theoperating system acts as manager of resources –hardware and software – required solve a problem.A control program manages the execution of userprograms to prevent errors and improper use of thecomputer. It is especially concerned with the controlof I/O devices.

The fundamental goal of operating system to executeuser programs and to make solving user problemseasier.When number of users conflicting request forresources then OS decides how to allocate them tospecific program and users so that computer canwork efficiently and fairly.

CASE STUDYLinux Linux Operating System has primarily threecomponents Kernel Kernel is the core part of Linux. It isresponsible for all major activities of thisoperating system. It consists of various modulesand it interacts directly with the underlyinghardware. Kernel provides the requiredabstraction to hide low level hardware details tosystem or application programs.

System Library System libraries are specialfunctions or programs using which applicationprograms or system utilities accesses Kernel'sfeatures. These libraries implement most of thefunctionalities of the operating system and do notrequires kernel module's code access rights. System Utility System Utility programs areresponsible to do specialized, individual leveltasks.

Windows 7Objectives: learn about main features in eachWindows 7 edition and what are minimumhardware requirements Prerequisites: no prerequisites. Key terms: windows 7 editions, starter, homebasic, home premium, professional, enterprise,ultimate, hardware requirements, processorarchitecture.

There are six different Windows 7 editions: Starter Home Basic Home Premium Professional Enterprise Ultimate

An operating system is a control program. It controls the execution of user programs to prevent errors and improper use of the computer. The Primary goal of operating system is convenience for the user. The operating system makes the use of system easier. The secondary goal of operating system is efficient operation of the computer system.

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