TOPIC 1. Following are some of important functions of an operating System. Memory Management. Processor Management. Device Management.

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1 TOPIC 1 An operating System (OS) is an intermediary between users and computer hardware. It provides users an environment in which a user can execute programs conveniently and efficiently. In technical terms, it is software which manages hardware. An operating System controls the allocation of resources and services such as memory, processors, devices and information. Definition An operating system is a program that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs. Following are some of important functions of an operating System. Memory Management Processor Management Device Management File Management Security

2 Control over system performance Job accounting Error detecting aids Coordination between other software and users Memory Management Memory management refers to management of Primary Memory or Main Memory. Main memory is a large array of words or bytes where each word or byte has its own address. Main memory provides a fast storage that can be access directly by the CPU. So for a program to be executed, it must in the main memory. Operating System does the following activities for memory management. Keeps tracks of primary memory i.e. what part of it are in use by whom, what part are not in use. In multiprogramming, OS decides which process will get memory when and how much. Allocates the memory when the process requests it to do so. De-allocates the memory when the process no longer needs it or has been terminated. Processor Management In multiprogramming environment, OS decides which process gets the processor when and how much time. This function is called process scheduling. Operating System does the following activities for processor management. Keeps tracks of processor and status of process. Program responsible for this task is known as traffic controller. Allocates the processor (CPU) to a process. De-allocates processor when processor is no longer required.

3 Device Management OS manages device communication via their respective drivers. Operating System does the following activities for device management. Keeps tracks of all devices. Program responsible for this task is known as the I/O controller. Decides which process gets the device when and for how much time. Allocates the device in the efficient way. De-allocates devices. File Management A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. Operating System does the following activities for file management. Keeps track of information, location, uses, status etc. The collective facilities are often known as file system. Decides who gets the resources. Allocates the resources. De-allocates the resources. Other Important Activities Following are some of the important activities that Operating System does. Security -- By means of password and similar other techniques, preventing unauthorized access to programs and data. Control over system performance -- Recording delays between request for a service and response from the system.

4 Job accounting -- Keeping track of time and resources used by various jobs and users. Error detecting aids -- Production of dumps, traces, error messages and other debugging and error detecting aids. Coordination between other software and users -- Coordination and assignment of compilers, interpreters, assemblers and other software to the various users of the computer systems. Evolution of Operating Systems The evolution of operating systems is directly dependent to the development of computer systems and how users use them. Here is a quick tour of computing systems through the past fifty years in the timeline. Early Evolution 1945: ENIAC, Moore School of Engineering, University of Pennsylvania. 1949: EDSAC and EDVAC 1949 BINAC - a successor to the ENIAC 1951: UNIVAC by Remington 1952: IBM : The interrupt : FORTRAN was developed Operating Systems by the late 1950s By the late 1950s Operating systems were well improved and started supporting following usages : It was able to Single stream batch processing It could use Common, standardized, input/output routines for device access Program transition capabilities to reduce the overhead of starting a new job was added Error recovery to clean up after a job terminated abnormally was added. Job control languages that allowed users to specify the job definition and resource requirements were made possible.

5 Operating Systems In 1960s 1961: The dawn of minicomputers 1962 Compatible Time-Sharing System (CTSS) from MIT 1963 Burroughs Master Control Program (MCP) for the B5000 system 1964: IBM System/ s: Disks become mainstream 1966: Minicomputers get cheaper, more powerful, and really useful : The mouse 1964 and onward: Multics 1969: The UNIX Time-Sharing System from Bell Telephone Laboratories Supported OS Features by 1970s Multi User and Multi tasking was introduced. Dynamic address translation hardware and Virtual machines came into picture. Modular architectures came into existence. Personal, interactive systems came into existence. Accomplishments after : Intel announces the microprocessor 1972: IBM comes out with VM: the Virtual Machine Operating System 1973: UNIX 4th Edition is published 1973: Ethernet 1974 The Personal Computer Age begins 1974: Gates and Allen wrote BASIC for the Altair 1976: Apple II August 12, 1981: IBM introduces the IBM PC 1983 Microsoft begins work on MS-Windows 1984 Apple Macintosh comes out 1990 Microsoft Windows 3.0 comes out

6 1991 GNU/Linux 1992 The first Windows virus comes out 1993 Windows NT 2007: ios 2008: Android OS And the research and development work still goes on, with new operating systems being developed and existing ones being improved to enhance the overall user experience while making operating systems fast and efficient like they have never been before. Types of Operating Systems Operating systems are there from the very first computer generation. Operating systems keep evolving over the period of time. Following are few of the important types of operating system which are most commonly used. Batch operating system The users of batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. Thus, the programmers left their programs with the operator. The operator then sorts programs into batches with similar requirements. The problems with Batch Systems are following. Lack of interaction between the user and job. CPU is often idle, because the speeds of the mechanical I/O devices are slower than CPU.

7 Difficult to provide the desired priority. Time-sharing operating systems Time sharing is a technique which enables many people, located at various terminals, to use a particular computer system at the same time. Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing. The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of multiprogrammed batch systems, objective is to maximize processor use, whereas in Time-Sharing Systems objective is to minimize response time. Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receive an immediate response. For example, in a transaction processing, processor execute each user program in a short burst or quantum of computation. That is if n users are present, each user can get time quantum. When the user submits the command, the response time is in few seconds at most. Operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time. Computer systems that were designed primarily as batch systems have been modified to time-sharing systems. Advantages of Timesharing operating systems are following Provide advantage of quick response. Avoids duplication of software. Reduces CPU idle time. Disadvantages of Timesharing operating systems are following.

8 Problem of reliability. Question of security and integrity of user programs and data. Problem of data communication. Distributed operating System Distributed systems use multiple central processors to serve multiple real time application and multiple users. Data processing jobs are distributed among the processors accordingly to which one can perform each job most efficiently. The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems. Processors in a distributed system may vary in size and function. These processors are referred as sites, nodes, and computers and so on. The advantages of distributed systems are following. With resource sharing facility user at one site may be able to use the resources available at another. Speedup the exchange of data with one another via electronic mail. If one site fails in a distributed system, the remaining sites can potentially continue operating. Better service to the customers. Reduction of the load on the host computer. Reduction of delays in data processing.

9 Network operating System Network Operating System runs on a server and and provides server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks. Examples of network operating systems are Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux, Mac OS X, Novell NetWare, and BSD. The advantages of network operating systems are following. Centralized servers are highly stable. Security is server managed. Upgrades to new technologies and hardware can be easily integrated into the system. Remote access to servers is possible from different locations and types of systems. The disadvantages of network operating systems are following. High cost of buying and running a server. Dependency on a central location for most operations. Regular maintenance and updates are required. Real Time operating System

10 Real time system is defines as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment. Real time processing is always on line whereas on line system need not be real time. The time taken by the system to respond to an input and display of required updated information is termed as response time. So in this method response time is very less as compared to the online processing. Real-time systems are used when there are rigid time requirements on the operation of a processor or the flow of data and real-time systems can be used as a control device in a dedicated application. Real-time operating system has well-defined, fixed time constraints otherwise system will fail. For example Scientific experiments, medical imaging systems, industrial control systems, weapon systems, robots, and home-appliance controllers, Air traffic control system etc. There are two types of real-time operating systems. Hard real-time systems Hard real-time systems guarantee that critical tasks complete on time. In hard real-time systems secondary storage is limited or missing with data stored in ROM. In these systems virtual memory is almost never found. Soft real-time systems Soft real time systems are less restrictive. Critical real-time task gets priority over other tasks and retains the priority until it completes. Soft real-time systems have limited utility than hard real-time systems. For example, Multimedia, virtual reality, Advanced Scientific Projects like undersea exploration and planetary rovers etc.

11 MULTIPROGRAMMING BATCH SYSTEMS In this the operating system, picks and begins to execute one job from memory. Once this job needs an I/O operation operating system switches to another job (CPU and OS always busy). Jobs in the memory are always less than the number of jobs on disk(job Pool). If several jobs are ready to run at the same time, then system chooses which one to run (CPU Scheduling). In Non-multiprogrammed system, there are moments when CPU sits idle and does not do any work. In Multiprogramming system, CPU will never be idle and keeps on processing. Time-Sharing Systems are very similar to Multiprogramming batch systems. In fact time sharing systems are an extension of multiprogramming systems. In time sharing systems the prime focus is on minimizing the response time, while in multiprogramming the prime focus is to maximize the CPU usage. MULTIPROCESSOR SYSTEMS A multiprocessor system consists of several processors that share a common physical memory. Multiprocessor system provides higher computing power and speed. In multiprocessor system all processors operate under single operating system. Multiplicity of the processors and how they do act together are transparent to the others. Following are some advantages of this type of system. 1. Enhanced performance 2. Execution of several tasks by different processors concurrently, increases the system's throughput without speeding up the execution of a single task.

12 3. If possible, system divides task into many subtasks and then these subtasks can be executed in parallel in different processors. Thereby speeding up the execution of single tasks. DISTRIBUTED OPERATING SYSTEMS The motivation behind developing distributed operating systems is the availability of powerful and inexpensive microprocessors and advances in communication technology. These advancements in technology have made it possible to design and develop distributed systems comprising of many computers that are inter connected by communication networks. The main benefit of distributed systems is its low price/performance ratio. Following are some advantages of this type of system. 1. As there are multiple systems involved, user at one site can utilize the resources of systems at other sites for resource-intensive tasks. 2. Fast processing. 3. Less load on the Host Machine. Cluster System Introduction What is a cluster? A cluster (as it pertains to computers) refers to a group of servers and other resources that are connected through hardware, networks and software to behave as if they were a single system. There are many reasons this is an attractive thing to do, even for smaller enterprises. These reasons include: high availability, load balancing, parallel processing, systems management and scalability. We'll talk more about each of these applications later in this course. But the main thing to understand right now about clustering is that its goal is to make a group of computers appear (to the outside world and to internal user

13 departments) as if they were one, totally integrated system that is always available and always working fast! Why are clusters so important? High Availability: The need to have core systems and their concomitant Web front-end servers running literally all the time means that high availability is imperative. This is where clustering is a brilliant solution. Clustering provides transparent backup and failover, and delivers redundancy of systems, peripherals and data all of which are critical to sustaining a 24x7x365 IS arena. Server Integration: Additionally, a Web-based business environment also means that enterprises can no longer expect a single, gigantic "computer in the sky" to solve all its processing needs even though a server can probably be purchased to handle a company's total "volumes" (in regard to data storage, etc.). Many applications require that the server resources be tweaked in different ways to achieve various purposes. Generally, there are three classes of workloads that require different server dynamics: Data transaction servers manage core business processes. Web application servers manage the end-user experience. Appliance servers manage specific network functions.

14 MSBTE QUESTION ANSWERS 1.With neat diagram, explain real time system. List its any four application. 4 M ANS: A real time system has well defined fixed time constraints. Processing should be done within the Defined constraints. Types of real time system Hard and Soft real time system. Satellite Application of real time OS: Satellite application of real time OS The satellite connected to the computer system sends the digital samples at the rate of 1000 samples per second. The computer system has an application program that stores these samples in a file. The sample sent by the satellite arrives every millisecond to the application. So computer must store or respond the sample in less than 1 millisecond. If the computer does not respond to the sample within this time, the sample will lost. Applications: 1. Flight Control System 2. Simulations 3. Industrial control 4. Military applications 2.Describe first generation of operating system with its advantages and disadvantages. 4M ANS: First generation vacuum tubes, plug boards: The earliest electronic digital computers had no operating systems. Machines of the time were so primitive that programs were often entered one bit at time on rows of mechanical switches (plug boards). Programming languages were unknown (not even assembly languages). Advantages:

15 That was the only electronic during those old days. Those computers were very fast to calculate. Vacuum tube technology made possible the advent of electronic digital computers. Use of vacuum tube technology made possible to make electronic digital computer. These computers could calculate in milliseconds. Disadvantages: The computers were very larger in size They consumed a large amount of energy. They heated very soon due to thousands of vacuum tubes. They were not very reliable. Air conditioning is required. Constant maintenance was required. Not-portable. Costly commercial production. Very slow speed. Limited programming capabilities. Used machine language only. Used punch card for input. Not versatile and less accurate. 3.Explain multiprocessor system and its two types. 4M ANS: Multiprocessor Systems: Multiprocessor systems with more than on CPU in close communication.

16 Tightly coupled system processors share memory and a clock; communication usually takes Place through the shared memory. Symmetric multiprocessing (SMP): Each processor runs and identical copy of the operating system. Most modern operating systems support SMP Asymmetric multiprocessing: Each processor is assigned a specific task; master processor schedules and allocated work to slave processors. More common in extremely large systems. Many processes can run at once without performance deterioration. 4.Explain multiprogrammed O.S with suitable diagram. 4M ANS: Multiprogramming is a rudimentary form of parallel processing in which several programs are run at the same time on a uniprocessor. Since there is only one processor, there can be no true simultaneous execution of different programs. Instead, the operating system executes part of one program, then part of another, and so on. To the user it appears that all programs are executing at the same time. Why Multiprogramming? Multiprogramming needed for efficiency: Single user cannot keep CPU and I/O devices busy at all times. Multiprogramming organizes jobs (code and data) so CPU always has one to execute. A subset of total jobs in system is kept in memory. One job selected and run via job scheduling. When it has to wait (for I/O for example), OS switches to another job.

17 Multiprogramming is a technique used to utilize maximum CPU time by running multiple programs simultaneously. The execution begins with the first program and continues till an instruction waiting for a peripheral is reached, the context of this program is stored, and the second program in memory is given a chance to run. The process continued until all programs finished running. Multiprogramming has no guarantee that a program will run in a timely manner. Usually on a mainframe - the computer has a number of programs loaded into memory and the operating system switches quickly between them, processing a little bit of each one in turn. The high speed of the processor makes it seem like more than one program is being run at the same time. On a PC it is usually called multitasking. If the machine has the capability of causing an interrupt after a specified time interval, then the operating system will execute each program for a given length of time, regain control, and then execute another program for a given length of time, and so on. In the absence of this mechanism, the operating system has no choice but to begin to execute a program with the expectation, but not the certainty, that the program will eventually return control to the operating system. If the machine has the capability of protecting memory, then a bug in one program is less likely to interfere with the execution of other programs. In a system without memory protection, one program can change the contents of storage assigned to other programs or even the storage assigned to the operating system. The resulting system crashes are not only disruptive, they may be very difficult to debug since it may not be obvious which of several programs is at fault. If memory can hold several programs, then CPU can switch to another one whenever a program is awaiting for an I/O to complete. 5.List different types of operating systems. Explain advantages of multiprocessor system (anytwo) ANS: Different types of operating systems: Mainframe systems Multiprocessor systems Clustered systems Distributed systems Real time systems Advantages of multiprocessor system:

18 Less time duration required for the large process. Economy of scale. Increased reliability. 6.Define multiprogramming system with diagram. ANS: In multiprogramming, more than one program lies in the memory i.e. in terms of Operating system, the scheduler selects the jobs to be placed in ready queue from a number of programs. The ready queue is placed in memory and the existence of more than one program in main memory is known as multiprogramming. Since there is only once processor, there can be no simultaneous execution of different programs. Instead the operating system executes part of one program, then the part of another and so on. Multiprogramming is the simple form of parallel processing in which several programs run at the same time on a processor. Example of multiprogramming, we open word, excel, access and other applications together but while we type in word other applications such as excel and access are just present in main memory but they are not performing any task or work. Or we can say that are not being

19 7.What is clustered system? Explain it. (Definition - 2 Marks, Explanation - 2 Marks) Ans: Clustered System: Cluster is a group of interconnected, whole computers working together as a unified computing source that can create the illusion of being one machine. Each computer in a cluster is typically referred to as a node. Clustering (means gather together) allows two or more system to share storage closely linked via a local area network. Asymmetric Cluster (at least two servers: One is on a standby mode while the other is monitoring the other one. If one stops other will work).symmetric Cluster (all work at the same level: They work together and monitor each other). Cluster is collection of computer in which any member of the cluster is capable of supporting the processing function of any other member. A cluster has n+k configuration where n processing nodes are actively processing the application & k processing nodes are in a standby state, serving as a spares. In the event of a failure of an active node, the application that was running on the failed node is moved to one of the standby nodes. Other common cluster configuration include Simplex (one active node, no spare), n+1 active node (n active nodes, 1 spare) Clustered system can be implemented using LAN.This system is a subsystem of a telecommunication switching system, running certain centralized application function. A LAN is interconnecting hub that provides connectivity with each other in the switching system. 8.List any four functions of operating system. (Any four functions - 1 mark each) Ans: The major functions of an operating system are: 1. Resource Management : This function of OS allocates computer resources such as CPU time, main memory, secondary storage and input and output devices for use. 2. Data management: It observes input and output of the data and their location, storage and retrieval. 3. Task management: Task is a collection of one or more related programs and their data. This function prepares, schedules, controls and monitors jobs submitted for execution to ensure the most efficient processing. 4. Allocation of Resources: Handles system resources such as computer's memory and sharing of the central processing unit (CPU) time by various applications or peripheral devices 5. Communication between User and Computer : Provides a user interface, e.g. command line, graphical user interface (GUI) 6. Operating system enables startup application programs. OS must have text editor, a translator and an editor.

20 7. Operating system provides number of services such as for the programmer it provides utilities ie debugger, editors, file management which refers to the way that the operating system manipulates, stores, retrieves and saves data. It interprets the commands executed by the user. It handles disk input/output settings. OR 1. Process Management Managing the programs that are running. 2. Memory Management Managing and rationing the memory between processes and data. 3. Storage Management Managing the permanent Storage of data on disks or other media 4. I/O Management Managing the input and output 5. Device / Resource Management Managing devices and resources and allowing the users to share the resources 6. Security and Protection Securing the system against possible unauthorized access to data or any other entity. Protecting the parts of the system against damage. 7. Booting the System and getting it ready to work. 8. Data communications Providing interface to connect to other computers or allowing others to connect 9.Describe real time operating system in brief. (Description of real time operating system - 4 marks; [Types optional]) Ans: Real time systems are used in environment where a large number of events, mostly external to the computer system, must be accepted and processes in a short time or within certain deadlines. Such applications include real-time simulations, flight control, industrial control, military applications etc. A primary objective of real-time systems is to provide quick event response time and thus meet the scheduling deadlines. User convenience and resource utilization are of secondary concern to realtime system designers. In Real time systems, processor is allocated to the highest priority process among those that are ready to execute. Higher priority processes preempt execution of the lower priority processes. This form is called as priority based preemptive scheduling. The primary functions of the real time operating system are to: 1. Manage the processor and other system resources to meet the requirements of an application. 2. Synchronize with and respond to the system events. 3. Move the data efficiently among processes and to perform coordination among these processes. Types of real time system: 1. Hard real time:- Hard real time means strict about adherence to each task deadline. When an event occurs, it should be serviced within the predictable time at all times in a given hard real time system. Example: -video transmission, each picture frame and audio must be transferred at fixed rate. 2. Soft real time:- Soft real time means that only the precedence and sequence for the task operations are defined, interrupt latencies and context switching latencies are small. There can be few deviations between

21 expected latencies of the tasks and observed time constraints and a few deadline misses are accepted. Example: - Mobile phone, digital cameras and orchestra playing robots. 10.Describe evolution of operating system. (Explanation of four generations - 1 mark each) [**Note - marks shall be given for generations or types of operating system**] Ans: Generations of operating system 1. The 1940's - First Generations 2. The 1950's - Second Generation 3. The 1960's - Third Generation 4. The 1980 s-the Fourth Generation First generation vacuum tubes, plug boards The earliest electronic digital computers had no operating systems. Machines of the time were so primitive that programs were often entered one bit at time on rows of mechanical switches (plug boards). Programming languages were unknown (not even assembly languages). The 1950's - Second Generation Second generation transistors, batch systems. By the early 1950's, the routine had improved somewhat with the introduction of punch cards. The General Motors Research Laboratories implemented the first operating systems in early 1950's for their IBM 701. The system of the 50's generally ran one job at a time. These were called single-stream batch processing systems because programs and data were submitted in groups or batches. The 1960's - Third Generation Third generation ICs and multiprogramming. The systems of the 1960's were also batch processing systems, but they were able to take better advantage of the computer's resources by running several jobs at once. So operating systems designers developed the concept of multiprogramming in which several jobs are in main memory at once; a processor is switched from job to job as needed to keep several jobs advancing while keeping the peripheral devices in use. The Fourth Generation Fourth generation 1980 present personal computers With the development of LSI (Large Scale Integration) circuits, chips, operating system entered in the system entered in the personal computer and the workstation age. Microprocessor technology evolved to the point that it becomes possible to build desktop computers as powerful as the mainframes of the 1970s.