disk scheduling

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Disk scheduling is one of the main responsibilities of Operating System. OS manages hard disk to provide best access time. All major Disk scheduling algorithms incorporate seek time as the only factor for disk scheduling. The second factor rotational delay is ignored by the existing algorithms. This research paper considers both factors, Seek Time and Rotational Delay to schedule the disk. Files are the most obvious objects in the operating systems manipulate. Everything is typically stored in files: programs, data, output, and so on. One problem in the file management is how to allocate space for file so that disk space is utilized effectively and files can be accessed quickly. Three major methods of allocating disk space are contiguous, linked and indexed. Each method has its advantages and disadvantages. Disk subsystem performance can be dramatically improved by dynamically ordering, or scheduling, pending re-quests. Via strongly validated simulation, we examine the impact of complex logical-to-physical mappings and large pre fetching caches on scheduling electiveness. Hard disks are being used to store huge information/data in all modem computers. Disk drives must provide faster access time in order to optimize speed of I/O operations. This paper describes development of a simulator which uses four disk scheduling algorithms (FCFS, SSTF, LOOK for both upward and downward direction, and C-LOOK) to measure their performance in terms of total head movement.
There are two objectives for any disk scheduling algorithm:
 Minimize the throughput - the average number of requests satisfied per time unit.
 Maximize the response time - the average time that a request must wait before it is satisfied

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