lecture27-chapter12 - OperatingSystems...

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Operating Systems Lecture 27 (wow, we made it!): File Management Anda Iamnitchi [email protected] 1
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The Big Picture, Again 2
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Review: Terms Four terms are in common use when discussing files: Field Record File: a collection of similar records is treated as a single entity by users and applications may be referenced by name Database: one or more files
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Review: Disk Geometry Disks consist of platters , each with two surfaces . Each surface consists of concentric rings called tracks . Each track consists of sectors separated by gaps . spindle surface tracks track k sectors gaps
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Blocks and records Records are the logical unit of access of a structured file Blocks are the unit of I/O on secondary storage For I/O to be performed, records must be organized as blocks
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Blocks and records Three approaches are common Fixed length blocking Variable length spanned blocking Variable length unspanned blocking
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Fixed Blocking Fixed length records are used, and an integral number of records are stored in a block. Unused space at the end of a block is internal fragmentation
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Variable Length Spanned Blocking Variable length records are used and are packed into blocks with no unused space. Some records may span multiple blocks Continuation is indicated by a pointer to the successor block
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Variable length unspanned blocking Uses variable length records without spanning Wasted space in most blocks because of the inability to use the remainder of a block if the next record is larger than the remaining unused space.
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The Big Picture, Again 10
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The Operating System is responsible for allocating blocks to files Two related issues How to allocate space to files?
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This note was uploaded on 02/18/2012 for the course COP 4600 taught by Professor Andaiamnitchi during the Fall '08 term at University of South Florida.

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lecture27-chapter12 - OperatingSystems...

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