week10_friday - CSCC 69H3 Operating Systems Spring 2010...

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Unformatted text preview: CSCC 69H3 Operating Systems Spring 2010 Professor Bianca Schroeder U of T Will return and go over midterm today Questions on your midterm: Come to my office after class 3-3:30pm Questions on A3? Come to my office Monday 11-12 or in the afternoon Brief announcement How does the OS implement the abstraction of files and directories? Files and directories … Disk Layout Strategies Files span multiple disk blocks How do you allocate the blocks for a file? 1. Contiguous allocation Contiguous Allocation 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 File Name Start Blk Length File A 2 3 File B 9 5 File C 18 8 File D 27 2 directory Disk Disk Layout Strategies Files span multiple disk blocks How do you find all of the blocks for a file? 1. Contiguous allocation Like memory Fast, simplifies directory access Inflexible, causes fragmentation, needs compaction 2. Linked, or chained, structure Linked Allocation 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 File Name Start Blk Last Blk … … … File B 1 22 … … … directory Disk Layout Strategies Files span multiple disk blocks How do you find all of the blocks for a file? 1. Contiguous allocation Like memory Fast, simplifies directory access Inflexible, causes fragmentation, needs compaction 2. Linked, or chained, structure Each block points to the next, directory points to the first Good for sequential access, bad for all others 3. Indexed structure (indirection, hierarchy) An “index block” contains pointers to many other blocks Handles random better, still good for sequential May need multiple index blocks (linked together) Indexed Allocation: Unix Inodes Unix inodes implement an indexed structure for files Each inode contains 15 block pointers...
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This note was uploaded on 05/22/2010 for the course CS CSCC69 taught by Professor Bianca during the Spring '10 term at University of Toronto.

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week10_friday - CSCC 69H3 Operating Systems Spring 2010...

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