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Highest response ratio next (HRRN) scheduling is a non-preemptive discipline. It was developed by Brinch Hansen as modification of shortest job next or shortest job first (SJN or SJF) to mitigate the problem of process starvation. In HRRN, the next job is not that with the shortest estimated run time, but that with the highest response ratio ...
Earliest deadline first (EDF) or least time to go is a dynamic priority scheduling algorithm used in real-time operating systems to place processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline.
Some preemptive multitasking scheduling systems behave as run-to-completion schedulers in regard to scheduling tasks at one particular process priority level, at the same time as those processes still preempt other lower priority tasks and are themselves preempted by higher priority tasks.
Windows 9x used non-preemptive multitasking for 16-bit legacy applications, and the PowerPC Versions of Mac OS X prior to Leopard used it for classic applications. [1] NetWare, which is a network-oriented operating system, used cooperative multitasking up to NetWare 6.5. Cooperative multitasking is still used on RISC OS systems. [3]
The algorithms used in scheduling analysis “can be classified as pre-emptive or non-pre-emptive". [1] A scheduling algorithm defines how tasks are processed by the scheduling system. In general terms, in the algorithm for a real-time scheduling system, each task is assigned a description, deadline and an identifier (indicating priority). The ...
Dynamic priority scheduling is a type of scheduling algorithm in which the priorities are calculated during the execution of the system. The goal of dynamic priority scheduling is to adapt to dynamically changing progress and to form an optimal configuration in a self-sustained manner.
Least slack time (LST) scheduling is an algorithm for dynamic priority scheduling. It assigns priorities to processes based on their slack time. Slack time is the amount of time left after a job if the job was started now. This algorithm is also known as least laxity first.
There is no universal best scheduling algorithm, and many operating systems use extended or combinations of the scheduling algorithms above. For example, Windows NT/XP/Vista uses a multilevel feedback queue, a combination of fixed-priority preemptive scheduling, round-robin, and first in, first out algorithms. In this system, threads can ...