Operating Systems

These are following Notes 

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Scheduling

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  Scheduling:              Scheduling is a fundamental operating system function. All computer resources are scheduled before use. Since Microprocessor is one of the primary computer resources, its scheduling is central operating system design. Scheduling refers to a set of policies and mechanisms supported by operating system that controls the order in which the work to be done is completed. A scheduler is an operating system program that selects the next job to be admitted for execution. The main objective of scheduling is to increase CPU utilization and higher throughput is the amount of work accomplished in a given time interval. CPU scheduling is the basis of operating system which supports multiprogramming concepts. By having a number of programs in computer memory at the same time, the CPU may be shared among them. This mechanism improves the overall efficiency of the computer system by getting more work done in less...
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Scheduling (Algorithms) Policies (Priority)

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Scheduling (Algorithms) Policies (Priority): These are the following different types  of common policies or algorithms: 1)       First Come First Served (FCFS) scheduling: This is non-preemptive technique. A single queue of ready processes is maintained, and the dispatcher always picks the first one. This method does not emphasize throughput, since long processes are allowed to monopolize CPU, For the same reason, the response time with FCFS can be high (with respect to execution time), especially if there is a high variance in process execution times. This is also known FCFS scheduling. Consider the following example of two processes- In the several processes come on different job p1, p2 and p3 respectively, here p2 and p3 jobs required less than or comparatively p1 process (job), but computer run p1 process in the process of FCFS scheduler. P2 and p3 process has in ready queue in waiting process state. Advantages: These are the following advantag...
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classification of operating System

  Types of Operating System: There are many different Operating Systems. But operating systems are mainly classified in several categories. These are the following – 1)       Single user and single tasking operating system   2)       Single user and multitasking operating system 3)       Multiuser multitasking Operating System   1) Single user single tasking operating system: This operating system is very popular on personal computers. In this system one user works on a machine at a time. One program can be executed at a time. So this operating system is known as ‘Single user operating system’. If you have a large number of jobs to be executed on such a system, then you have to execute them one after another in sequence. For example: Input and output devices like the printer are very slow as compared to the speed of a CPU. When, you give the printing command a CPU reads a file ...
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What is an operating System

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  What is an operating System?             An operating system is an essential component of a computer system. The primary objectives of an operating system are to make computer system suitable to use and utilized computer hardware. An operating system is a program designed to run other programs on a computer. A computer’s operating system is its most important program. It is considered the backbone of a computer, managing both software and hardware resources. Operating systems are responsible for everything from the control and allocation of memory to recognizing input from external devices and transmitting output to computer displays. They also manage files on computer hard drives and control peripherals, like printers and scanners. The operating system of a large computer system has even more work to do. Such operating systems monitor different programs and users, making sure everything runs smoothly, without interference,...
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Inter-process Communication and Process Synchronization

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  Inter-process Communication and Process Synchronization:             Inter-process communication is a set of programming interfaces that allow a programmer to coordinate activities among different program processes that can run concurrently in an operating system. There are applications that involve each executing multiple processes concurrently. Processes work together to perform application-specific tasks. They are referred to as cooperating processes. Cooperating processes are “loosely” connected in the sense that they have independent private address spaces and run at different speeds. The relative speeds of the processes are not normally known. From time to time, they interact among themselves by exchanging information. An exchange of information among processes is called an interposes communication.             It is stated in that one process cannot access elem...
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Functions of Operating System

  Functions of Operating System: There are many functions those are performed by the operating system, but the main goal of operating system is to provide the interface between the user and the hardware means provides the interface for working on the system by the user. The various functions those are performed by the operating system, these are the following:- 1)       Input/ Output device management: In a process program takes an input and then produces an output. It takes the input through input devices and produces output through output devices. Thus, it has to handle input and output devices during program execution. It is very tedious to write instructions to directly handle the input and output devices through the user program. Therefore operating system provides device driver to handle input and output devices. Programmers can user these derivers in their program to control the input/output devices. The interaction of the program wit...
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Batch Operating System

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Batch Operating System : In the early days this system was used. Those days,  the jobs were placed in a job queue and the memory allocate managed the primary memory space, when space was available in the main memory, a job was selected from the job queue and it was loaded into memory. Once the job loaded into primary memory, it competes for the processor. When the processor became available, the processor scheduler selects job that was loaded in the memory and execute it. In batch processing is implemented to provide a batch file processing. So in this approach files of the similar batch are processed to speed up the task. It resulted in improved system utilization and performance of machine,  due to reduced turnaround time of execution job.               In batch processing system, earlier the jobs were scheduled in the order of their arrival that first comes first out(FIFO) / FCFS.  This scheduling method was easy and simple to i...
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