06-resource-management

06-resource-management - Operating Systems: Resource...

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Operating Systems: Resource Management CSE 110: Introduction to Computer Science
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Resource Management Processes (programs) require resources (disks, printers, RAM, etc.) to execute Sometimes, there isn’t enough of a resource to go around The operating system is responsible for allocating resources to programs fairly, so that each one has a chance to execute
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Managing Resources Disk I/O requests System memory (RAM) 5 MB hard disk, circa 1956
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What’s in a Hard Disk? A hard disk consists of a stack of platters Platter: thin disk with a magnetic coating Read/write heads store and retrieve data Disks are divided into tracks (concentric rings) and sectors (small arcs within tracks) A stack of sectors is a cylinder
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Disk Requests The time needed to retrieve a piece of data from a disk is broken down into three components 1. Seek time time needed to move the disk head between tracks 2. Latency (rotational delay) time needed for the disk to revolve into position 3. Transfer rate the rate at which data can be read from/written to the disk On a clear disk, you can seek forever. — Anon.
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Disk Scheduling Algorithms As programs request access to the disk, their requests (disk locations to be read/written) are placed in a list or queue The operating system uses one or more strategies to decide which request to service next These strategies vary in efFciency and fairness Goal: minimize disk head movement and how long a request must wait to be serviced
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Scheduling Strategies I First Come, First Served (FCFS) Disk requests are processed in the order that they arrived This is the most fair strategy in terms of waiting time The disk head may move a very long distance between requests, ignoring later requests that lie along the way
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Scheduling Strategies II Shortest Seek Time First (SSTF) Arrange all requests by their position on disk Select the next request to service based on how close it is to the current head position This guarantees the minimum head movement Distant requests may be starved in favor of late-arriving requests that are closer Solution tip: Write out all of the disk requests in order of address, and use this chart to find the closest one(s).
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This note was uploaded on 03/29/2012 for the course CSE 110 taught by Professor Shaunakpawagi during the Spring '08 term at SUNY Stony Brook.

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06-resource-management - Operating Systems: Resource...

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