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Scheduling algorithm for disk

Posted on 1998-10-08
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Last Modified: 2010-04-27
As disk technology improves, the seek time is becoming progressively shorter, and it may soon take less time to seek to the desired cylinder than it takes for the desired sector to rotate under the disk heads.
Under this circumstances, would it make sense to use any of the scheduling algorithm such as First come first serve to order requests for the same track. If so which algorithm is the best
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Question by:Novice100898
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mark2150 earned 70 total points
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Your circumstance can't happen. You can't determine what sector is flying by until *after* you've seeked and settled to desired cylinder. No matter how fast cylinder seek time is, your access time will always be this time *plus* a 1/2 rotation (on average)

Taccess.avg = Tseek + Trot / 2

Since majority of reads are sequential and RAM is cheap, cylinder buffering reduces "2nd read" latency by substantial margin. Controller reads entire track/cylnder in one gulp and heads can start seek of next cylnder while buffered data transfers out.

M
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by:Novice100898
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If the seek time become negigible and there is no caching in place, can we have an algorithm which will help to speed up the rate at which data is access. That is if the first request is at sector 3 track 2 and second request at sector 6 track 2 and third request at sector 8 track 2 and they are all in a queue, will it be possible to implement any algorithms to solve the problem.
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