\n| Process<\/b><\/td>\n | Arrival Time<\/b><\/td>\n | Execution Time<\/b><\/td>\n | Service Time<\/b><\/td>\n<\/tr>\n\n| P0<\/span><\/td>\n | 0<\/span><\/td>\n | 5<\/span><\/td>\n | 0<\/span><\/td>\n<\/tr>\n\n| P1<\/span><\/td>\n | 1<\/span><\/td>\n | 3<\/span><\/td>\n | 5<\/span><\/td>\n<\/tr>\n\n| P2<\/span><\/td>\n | 2<\/span><\/td>\n | 8<\/span><\/td>\n | 14<\/span><\/td>\n<\/tr>\n\n| P3<\/span><\/td>\n | 3<\/span><\/td>\n | 6<\/span><\/td>\n | 8<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Waiting time of each process:<\/strong><\/p>\n\n\n\n| Process<\/b><\/td>\n | Waiting Time = Service Time – Arrival Time<\/b><\/td>\n<\/tr>\n\n| P0<\/span><\/td>\n | 0 – 0 = 0<\/span><\/td>\n<\/tr>\n\n| P1<\/span><\/td>\n | 5 – 1 = 4<\/span><\/td>\n<\/tr>\n\n| P2<\/span><\/td>\n | 14 – 2 = 12<\/span><\/td>\n<\/tr>\n\n| P3<\/span><\/td>\n | 8 – 3 = 5<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Average Waiting Time = (0 + 4 + 12 + 5)\/4 = 21 \/ 4 = 5.25<\/p>\n Advantages:<\/h4>\n\n- Short processes execute first.<\/li>\n<\/ul>\n
Disadvantages:<\/h4>\n\n- There is a chance of starvation if short processes keep coming in the ready state.<\/li>\n<\/ul>\n
3. Priority Scheduling<\/h3>\nThis scheduling algorithm is commonly used in batch systems and is a non-preemptive scheduling algorithm. In this each process is assigned a priority and the process with the highest priority executes first followed by the ones lower in priority. If two processes share the same priority then execution is done on a first come first served basis. Priority is decided based on memory requirements, time requirements, or any other resource requirement.<\/p>\n \n\n\n| Process<\/b><\/td>\n | Arrival Time<\/b><\/td>\n | Execution Time<\/b><\/td>\n | Priority<\/b><\/td>\n | Service Time<\/b><\/td>\n<\/tr>\n\n| P0<\/span><\/td>\n | 0<\/span><\/td>\n | 5<\/span><\/td>\n | 1<\/span><\/td>\n | 0<\/span><\/td>\n<\/tr>\n\n| P1<\/span><\/td>\n | 1<\/span><\/td>\n | 3<\/span><\/td>\n | 2<\/span><\/td>\n | 11<\/span><\/td>\n<\/tr>\n\n| P2<\/span><\/td>\n | 2<\/span><\/td>\n | 8<\/span><\/td>\n | 1<\/span><\/td>\n | 14<\/span><\/td>\n<\/tr>\n\n| P3<\/span><\/td>\n | 3<\/span><\/td>\n | 6<\/span><\/td>\n | 3<\/span><\/td>\n | 5<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Waiting time of each process:<\/p>\n \n\n\n| Process<\/b><\/td>\n | Waiting Time<\/b><\/td>\n<\/tr>\n\n| P0<\/span><\/td>\n | 0 – 0 = 0<\/span><\/td>\n<\/tr>\n\n| P1<\/span><\/td>\n | 11 – 1 = 10<\/span><\/td>\n<\/tr>\n\n| P2<\/span><\/td>\n | 14 – 2 = 12<\/span><\/td>\n<\/tr>\n\n| P3<\/span><\/td>\n | 5 – 3 = 2<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Average Waiting Time = (0 + 10 + 12 + 2)\/4 = 24 \/ 4 = 6<\/p>\n Advantages:<\/h4>\n\n- Higher priority processes execute first.<\/li>\n<\/ul>\n
Disadvantages:<\/h4>\n\n- There is a chance of starvation if only higher priority processes keep coming in the ready state<\/li>\n
- If two processes have the same priorities, then some other scheduling algorithm needs to be used.<\/li>\n<\/ul>\n
4. Shortest Remaining Time (SRT)<\/h3>\nThis scheduling algorithm is the preemptive version of the SJN algorithm. The OS allocates the processor to the job that is closest to completion. Though there is a chance of this job being preempted, if another job is ready with a shorter time to completion. It is used in batch environments where short jobs are given preference and cannot be implemented in interactive systems where required CPU time is unknown.<\/p>\n 5. Round Robin (RR)<\/h3>\nThis scheduling algorithm is a preemptive process scheduling algorithm where each process is provided a fixed time to execute. This fixed time is called a quantum.It uses context switching to save states of preempted processes. Once a process is done executing for a given time period, it is preempted and another process executes for a given time period.<\/p>\n ![\"Round](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/08\/Round-Robin-RR.jpg\") <\/a><\/p>\nWaiting time of each process:<\/p>\n
\n\n\n| Process<\/b><\/td>\n | Waiting Time<\/b><\/td>\n<\/tr>\n\n| P0<\/span><\/td>\n | (0 – 0) +(12 – 3) = 9<\/span><\/td>\n<\/tr>\n\n| P1<\/span><\/td>\n | (3 – 1) = 2<\/span><\/td>\n<\/tr>\n\n| P2<\/span><\/td>\n | (6 – 2) + (14 – 9) + (20 – 17) = 12<\/span><\/td>\n<\/tr>\n\n| P3<\/span><\/td>\n | (9 – 3) + (17 – 12) = 11<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Average Waiting Time = (9+2+12+11) \/ 4 = 8.5<\/p>\n Advantages:<\/h4>\n\n- No starvation as every process gets a chance for its execution.<\/li>\n
- Used in time-sharing systems.<\/li>\n<\/ul>\n
Disadvantages:<\/h4>\n\n- The CPU is left idle due to a lot of context switching.<\/li>\n<\/ul>\n
6. Multiple-Level Queues<\/h3>\nIn this scheduling algorithm multiple algorithms with common characteristics come together to form a group and then schedule jobs as a whole. Thus, it is not an independent scheduling algorithm. There are multiple queues for processes with common characteristics and each queue has its own scheduling algorithms. The OS assigns priorities to each queue.<\/p>\n 7. Multilevel Feedback Queue<\/h3>\nThis scheduling algorithm is similar to multilevel queue scheduling except that the processes here can change their queue too i.e., if a process is in queue1, then after partial execution, it can switch to queue2.<\/p>\n There is a list of queues with different priorities and one with a higher priority queue executes first. During execution of a process with a higher priority queue comes, then the execution of the lower priority queue stops and the one with higher priority queue replaces it. There is a chance of starvation if the higher priority queue keeps coming in the ready state and the lower priority queue keeps waiting for its turn.<\/p>\n 8. Highest Response Ratio Next<\/h3>\nIn this scheduling algorithm, scheduling is done on the basis of response ratio. The process with the highest response ratio is scheduled next which reduces starvation in the system.<\/p>\n Purpose of a Scheduling algorithm<\/h3>\nThe purpose of a scheduling algorithm is to provide:<\/p>\n \n- Maximum CPU utilization<\/li>\n
- Minimum turnaround time<\/li>\n
- Fair allocation of CPU<\/li>\n
- Maximum throughput<\/li>\n
- Minimum waiting time<\/li>\n
- Minimum response time<\/li>\n<\/ul>\n
Summary<\/h3>\nScheduling algorithm schedules jobs. There are six types of algorithms that we have seen in this tutorial. Hope you liked it.<\/p>\n","protected":false},"excerpt":{"rendered":" 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...<\/p>\n","protected":false},"author":1,"featured_media":100220,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24565],"tags":[24913,24919,24918,24917,24912,24916,24911,24914,24915],"class_list":["post-99898","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-operating-system-tutorials","tag-first-come-first-serve","tag-highest-response-ratio-next","tag-multilevel-feedback-queue","tag-multiple-level-queues","tag-priority-scheduling","tag-round-robin","tag-scheduling-algorithms","tag-shortest-job-next","tag-shortest-remaining-time"],"yoast_head":"\n Scheduling Algorithms in Operating System - DataFlair<\/title>\n<meta name=\"description\" content=\"Scheduling algorithm schedules processes on the processor in an efficient and effective manner. 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![\"First-Come](\"https:\/\/data-flair.training\/blogs\/wp-content\/uploads\/sites\/2\/2021\/08\/First-Come-First-Served.jpg\")
<\/a><\/p>\n