Types of scheduler in os

We offer you a brighter future with FREE online courses Scheduling algorithms schedule processes on the processor in an efficient and effective manner. This scheduling is done by a Process Scheduler. It maximizes CPU utilization by increasing throughput. Following are the popular process scheduling algorithms about which we are going to talk in this chapter: 1. First-Come, First-Served (FCFS) Scheduling 2. Shortest-Job-Next (SJN) Scheduling 3. Priority Scheduling 4. Shortest Remaining Time 5. Round Robin(RR) Scheduling 6. Multiple-Level Queues Scheduling 7. Multilevel Feedback Queues Scheduling 8. Highest Response Ratio Next 1. First-Come, First-Served (FCFS) In this scheduling algorithm, jobs are executed on a first come, first serve basis irrespective of burst time or priority. It is both a preemptive and non-preemptive scheduling algorithm. It is based on the First In First Out (FIFO) queue. Waiting time of each process: Process Waiting Time = Service Time – Arrival Time P0 0 – 0 = 0 P1 5 – 1 = 4 P2 8 – 2 = 6 P3 16 – 3 = 13 Average Waiting Time = (0+4+6+13) / 4 = 5.75 Advantages of FCFS: • It is simple and easy to implement. Disadvantages of FCFS: • Inefficient throughput • If a process has a very high burst time and is coming first, then it will be executed first even if another process with a lesser time is present in the ready state. 2. Shortest Job Next (SJN) Also known as shortest job first (SJF), this scheduling algorithm is both a non-preemptive and preemptive sc...

\( \newcommand\) • • • • • • • • Scheduling Algorithms Scheduling algorithmsare used for distributing resources among parties which simultaneously and asynchronously request them. Scheduling disciplines are used in routers (to handle packet traffic) as well as in operating systems (to share CPU time among both threads and processes), disk drives (I/O scheduling), printers (print spooler), most embedded systems, etc. The main purposes of scheduling algorithms are to minimize resource starvation and to ensure fairness amongst the parties utilizing the resources. Scheduling deals with the problem of deciding which of the outstanding requests is to be allocated resources. There are many different scheduling algorithms. In this section, we introduce several of them. In packet-switched computer networks and other statistical multiplexing, the notion of a scheduling algorithm is used as an alternative to first-come first-served queuing of data packets. The simplest best-effort scheduling algorithms are round-robin, fair queuing (a max-min fair scheduling algorithm), proportionally fair scheduling and maximum throughput. If differentiated or guaranteed quality of service is offered, as opposed to best-effort communication, weighted fair queuing may be utilized. In advanced packet radio wireless networks such as HSDPA (High-Speed Downlink Packet Access) 3.5G cellular system, channel-dependent scheduling may be used to take advantage of channel state information. If the channel cond...

Overview CPU scheduling is the task performed by the CPU that decides the way and order in which processes should be executed. There are two types of CPU scheduling - Preemptive, and non-preemptive. The criteria the CPU takes into consideration while "scheduling" these processes are - CPU utilization, throughput, turnaround time, waiting time, and response time. Scope • In this article, we'll learn about CPU scheduling and its working. • We'll also go through its important terminology and needs of the TCPU scheduling. • We'll learn about the various CPU scheduling algorithms and comparisons between them. What is CPU Scheduling? Before we get to CPU scheduling, let's define a process. A process is essentially just a set of instructions or a program in execution. As you can see in the diagram above, we have processes that come from the job queue to the ready queue (in primary memory) that are one by one, in some manner given resources, and then their execution is completed. Say you have a uni programming system (like MS-DOS) and a process that requires I/O is being executed. While it waits for the I/O operations to complete, the CPU remains idle. This is wrong, because we're wasting the resources of the CPU, as well as time, and might result in some processes waiting too long for their execution. In multiprogramming systems, however, the CPU does not remain idle whenever a process currently executing waits for I/O. It starts the execution of other processes, making an attemp...

In the pre-emptive scheduling, the operating system can interrupt a running process and allocate the CPU to another process with a higher priority. This helps ensure that important tasks get completed quickly and efficiently. Now, we are going to cover about preemptive scheduling algorithm in operating System; involving with preemptive scheduling examples and its types with ease. This is unique article over the internet. So we make sure that at the end of this post; you will definitely fully educate about Preemptive Scheduling Algorithm without getting any hindrance. What is Preemptive Scheduling Algorithm? Preemptive scheduling is a CPU scheduling technique used in computer operating systems to ensure that the highest priority process gets access to the CPU (Central Processing Unit) as soon as it becomes available. In this scheduling, the operating system can interrupt a running process to allocate the CPU to a higher-priority process that needs it. This is in contrast to non-preemptive scheduling, where once a process has control of the CPU, it will continue to execute until it voluntarily releases the CPU or until it has completed its task. Preemptive scheduling allows to assign every process as a priority level, which determines its importance relative to other processes. The operating system will allocate the CPU to the process with the highest priority level that is currently ready to run. If a higher-priority process becomes ready to run while a lower-priority proce...

In real-time systems, the scheduler is considered as the most important component which is typically a short-term task scheduler. The main focus of this scheduler is to reduce the response time associated with each of the associated processes instead of handling the deadline. If a preemptive scheduler is used, the real-time task needs to wait until its corresponding tasks time slice completes. In the case of a non-preemptive scheduler, even if the highest priority is allocated to the task, it needs to wait until the completion of the current task. This task can be slow (or) of the lower priority and can lead to a longer wait. A better approach is designed by combining both preemptive and non-preemptive scheduling. This can be done by introducing time-based interrupts in priority based systems which means the currently running process is interrupted on a time-based interval and if a higher priority process is present in a ready queue, it is executed by preempting the current process. Based on schedulability, implementation (static or dynamic), and the result (self or dependent) of analysis, the scheduling algorithm are classified as follows. • Static table-driven approaches: These algorithms usually perform a static analysis associated with scheduling and capture the schedules that are advantageous. This helps in providing a schedule that can point out a task with which the execution must be started at run time. • Static priority-driven preemptive approaches: Similar to the...

• Login • Category • Java • JSP • iOS • HTML • Android • Python • C Programming • C++ Programming • C# • PHP • CSS • Javascript • jQuery • SAP • SAP HANA • Data Structure • RDBMS • MySQL • Mathematics • 8085 Microprocessor • Operating System • Digital Electronics • Analysis of Algorithms • Mobile Development • Front End • Web Development • Selenium • MongoDB • Computer Network • General Topics Let us begin by understanding what a scheduler is. Scheduler It is used for handling the process and makes scheduling for the process. The main task of the scheduler is to select the process and make order of process, and to decide which process runs first. Types of Schedulers There are three different types of schedulers, which are as follows − Long term scheduler Long term scheduling is performed when a new process is created, if the number of ready processes in the ready queue becomes very high, and then there is an overhead on the operating system, for maintaining long lists, containing switching and dispatching increases. Therefore, allowing only a limited number of processes into the ready queue, the long term scheduler manages this. The long term scheduler is given below − Medium term scheduler After execution then enters into input/ output operation state, then again comes back into a ready state. So, at that time a medium-term scheduler is used. The medium-term scheduler is given below − Short term scheduler All the processes are in a ready state, which process should run fi...

Scheduling Algorithms in OS (Operating System) There are various algorithms which are used by the Operating System to schedule the processes on the processor in an efficient way. The Purpose of a Scheduling algorithm • Maximum CPU utilization • Fare allocation of CPU • Maximum throughput • Minimum turnaround time • Minimum waiting time • Minimum response time There are the following algorithms which can be used to schedule the jobs. 1. First Come First Serve It is the simplest algorithm to implement. The process with the minimal arrival time will get the CPU first. The lesser the arrival time, the sooner will the process gets the CPU. It is the non-preemptive type of scheduling. 2. Round Robin In the Round Robin scheduling algorithm, the OS defines a time quantum (slice). All the processes will get executed in the cyclic way. Each of the process will get the CPU for a small amount of time (called time quantum) and then get back to the ready queue to wait for its next turn. It is a preemptive type of scheduling. 3. Shortest Job First The job with the shortest burst time will get the CPU first. The lesser the burst time, the sooner will the process get the CPU. It is the non-preemptive type of scheduling. 4. Shortest remaining time first It is the preemptive form of SJF. In this algorithm, the OS schedules the Job according to the remaining time of the execution. 5. Priority based scheduling In this algorithm, the priority will be assigned to each of the processes. The highe...

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In real-time systems, the scheduler is considered as the most important component which is typically a short-term task scheduler. The main focus of this scheduler is to reduce the response time associated with each of the associated processes instead of handling the deadline. If a preemptive scheduler is used, the real-time task needs to wait until its corresponding tasks time slice completes. In the case of a non-preemptive scheduler, even if the highest priority is allocated to the task, it needs to wait until the completion of the current task. This task can be slow (or) of the lower priority and can lead to a longer wait. A better approach is designed by combining both preemptive and non-preemptive scheduling. This can be done by introducing time-based interrupts in priority based systems which means the currently running process is interrupted on a time-based interval and if a higher priority process is present in a ready queue, it is executed by preempting the current process. Based on schedulability, implementation (static or dynamic), and the result (self or dependent) of analysis, the scheduling algorithm are classified as follows. • Static table-driven approaches: These algorithms usually perform a static analysis associated with scheduling and capture the schedules that are advantageous. This helps in providing a schedule that can point out a task with which the execution must be started at run time. • Static priority-driven preemptive approaches: Similar to the...

Scheduling Algorithms in OS (Operating System) There are various algorithms which are used by the Operating System to schedule the processes on the processor in an efficient way. The Purpose of a Scheduling algorithm • Maximum CPU utilization • Fare allocation of CPU • Maximum throughput • Minimum turnaround time • Minimum waiting time • Minimum response time There are the following algorithms which can be used to schedule the jobs. 1. First Come First Serve It is the simplest algorithm to implement. The process with the minimal arrival time will get the CPU first. The lesser the arrival time, the sooner will the process gets the CPU. It is the non-preemptive type of scheduling. 2. Round Robin In the Round Robin scheduling algorithm, the OS defines a time quantum (slice). All the processes will get executed in the cyclic way. Each of the process will get the CPU for a small amount of time (called time quantum) and then get back to the ready queue to wait for its next turn. It is a preemptive type of scheduling. 3. Shortest Job First The job with the shortest burst time will get the CPU first. The lesser the burst time, the sooner will the process get the CPU. It is the non-preemptive type of scheduling. 4. Shortest remaining time first It is the preemptive form of SJF. In this algorithm, the OS schedules the Job according to the remaining time of the execution. 5. Priority based scheduling In this algorithm, the priority will be assigned to each of the processes. The highe...