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Anticipatory Scheduling is a method of improving the performance of hard disk input/output.

In the area of IO scheduling, anticipatory scheduling overcomes "deceptive idleness" of the disk head, a situation where a process appears to be idle when viewed from the disk end, because a small delay between two fairly consecutive synchronous pieces of I/O will cause a normal work conserving disk scheduler to switch to unrelated I/O. This situation is detrimental to the throughput of synchronous, as it degenerates into a seeking workload thus causing a huge degradation in disk throughput.

The anticipatory scheduler (AS) was the default Linux kernel scheduler between 2.6.0 and 2.6.18, by which time it was replaced by the CFQ scheduler.

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