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Various scheduling policies can be used at queueing nodes: First in, first out First in first out (FIFO) queue example Also called first-come, first-served (FCFS), [21] this principle states that customers are served one at a time and that the customer that has been waiting the longest is served first. [22] Last in, first out
Common scheduling disciplines include the following: Random scheduling (RSS) First In, First Out , also known as First Come First Served (FCFS) Last In, First Out ; Shortest seek first, also known as Shortest Seek / Service Time First (SSTF) Elevator algorithm, also known as SCAN (including its variants, C-SCAN, LOOK, and C-LOOK)
Processes in the base level queue can also be scheduled on a first come first served basis. [6] Optionally, if a process blocks for I/O, it is promoted one level, and placed at the end of the next-higher queue. This allows I/O bound processes to be favored by the scheduler and allows processes to escape the base-level queue.
Such processing is analogous to servicing people in a queue area on a first-come, first-served (FCFS) basis, i.e. in the same sequence in which they arrive at the queue's tail. FCFS is also the jargon term for the FIFO operating system scheduling algorithm, which gives every process central processing unit (CPU) time in the order in which it is ...
Often it is assumed that the jobs within a class form a queue and that queue is served on a first-come, first-served basis, but this assumption is not necessary for many GPS applications. [1] In processor scheduling, generalized processor sharing is "an idealized scheduling algorithm that achieves perfect fairness. All practical schedulers ...
Customers are typically served on a first-come, first-served basis, other popular scheduling policies include processor sharing where all jobs in the queue share the service capacity between them equally; last-come, first served without preemption where a job in service cannot be interrupted
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The scheduler is an operating system module that selects the next jobs to be admitted into the system and the next process to run. Operating systems may feature up to three distinct scheduler types: a long-term scheduler (also known as an admission scheduler or high-level scheduler), a mid-term or medium-term scheduler, and a short-term scheduler.