By far the simplest CPU-scheduling algorithm is the first-come, first-served (FCFS) scheduling algorithm. With this scheme, the process that requests the CPU first is allocated the CPU first. The implementation of the FCFS policy is easily managed with a FIFO queue. When a process enters the ready queue, its PCB is linked onto the tail of the queue. When the CPU is free, it is allocated to the process at the head of the queue. The running process is then removed from the queue. The code for FCFS scheduling is simple to write and understand. The average waiting time under the FCFS policy, however, is often quite long. Consider the following set of processes that arrive at time 0, with the length of the CPU-burst time given in milliseconds:
SJhortest job First
Basically,this is a need in case of multiprogramming.For optimum utilization of CPU it should be utilised in the meanwhile time when some process is in waiting state for some I/O or waiting for some event to occur. So,for this many programs should be in memory in waiting state so that CPU can be allocated to some other process for optimum utilization of CPU. A schedule(time table in broad sense) which will decide Cpu will be allocated to which process when some previous process is in waiting state. Now this schedule is designed according to some criteria(algorithm) to decide CPU will be allocated to which process. Some Algorithms: 1.First Come First Serve(FCFS) 2.Shortest Job Scheduling(SJS) 3.RoundRobin Scheduling(RRS)
Cooperative schedulingPreemptive scheduling Rate-monotonic schedulingRound-robin schedulingFixed priority pre-emptive scheduling, an implementation of preemptive time slicingFixed-Priority Scheduling with Deferred PreemptionFixed-Priority Non-preemptive SchedulingCritical section preemptive schedulingStatic time schedulingEarliest Deadline First approachStochastic digraphs with multi-threaded graph traversal
>File systems must be accessed in an efficient manner >As a computer deals with multiple processors over a period of time, a list of request to access the disk build up >The operating system uses a disk scheduling technique to determine which request to satisfy. Disk scheduling techniques: (1)First-come, First-served (2)Shortest-seek-time-first(SSTF) (3)scan 4 c-scan 5
in fcfs scheduling there is a shortcoming that is if any rocess of maximum brust time is first ome. and after that many short burst time process come. then smaller pocesses have to wait for a long time untill the max brust time process complete their execution. in case of shortest job first it applied the method to give shortest t\burst time job to processer first.
its the algorithm that tells the os what to process next.goes according to :shortest job firstshortest remaining time firstround robin- first in first out system
A "first fit" algorithm is any algorithm which doesn't care about how "good" a solution is, it just returns the first one that works.
New requests for the track over which the head currently resides can theoretically arrive as quickly as these requests are being serviced
In that work system, the shortest job gets higher priority because more gets accomplished in any amount of time. If you have two hours to do 4 tasks and one task will take five minutes, one will take 30 minutes, one will take an hour and one will take an hour and a half, by using the shortest job first method, you will accomplish three tasks in those two hours and part of the fourth task. If you do the longest job first, you will accomplish the task that takes an hour and a half, then only part of the one hour task, but nothing on the 5 minute or 30 minute tasks. That means that by doing the shortest jobs first, you will accomplish three times as many tasks as you will by doing the longest jobs first.
Google's first -and historically major development- was its search engine's algorithm.
short job first (SJF) is a job scheduling algorithm where shorter jobs are favored for being serviced first. this increases the overall system's number of processed jobs but has the disadvantage that long jobs can face starvation in waiting state irrespective to their wait time..
Non pre-emptive means once CPU starts executing one process, it will not be taken out of the CPU until it is terminated or it has to wait for some event. In preemptive SJF scheduling, current running process is moved to the ready queue when a new process with a shorter CPU burst joins the ready queue.
First In First Out (FIFO) – This is the simplest page replacement algorithm. ...Optimal Page replacement – In this algorithm, pages are replaced which would not be used for the longest duration of time in the future. ...Least Recently Used – In this algorithm page will be replaced which is least recently used.First In First Out (FIFO) – This is the simplest page replacement algorithm. ...Optimal Page replacement – In this algorithm, pages are replaced which would not be used for the longest duration of time in the future. ...Least Recently Used – In this algorithm page will be replaced which is least recently used.
Step 1:- select first root node (t), start travelsing left contin
You can use a The Depth-First Search algorithm.
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FIFO (first in first out)