Lecture3

Lecture3 - COT 5611 Operating Systems Design Principles...

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COT 5611 Operating Systems Design Principles Spring 2010 Dan C. Marinescu Office: HEC 439 B Office hours: M-Wd 1:00-2:00 PM
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2 Names and the three basic abstractions ± Memory Î stores named objects ² write(name, value) value Å READ(name) ² file system: /dcm/classes/Fall09/Lectures/Lecture5.ppt ± Interpreters Î manipulates named objects ² machine instructions ADD R1,R2 ² modules Î Variables call sort(table) ± Communication Links Î connect named objects ² HTTP protocol used by the Web and file systems Host: boticelli.cs.ucf.edu put /dcm/classes/Fall09/Lectures/Lecture5.ppt get /dcm/classes/Fall09/Lectures/Lecture5.ppt
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3 Memory ± Hardware memory: ² Devices ± RAM (Random Access Memory) chip ± Flash memory Î non-volatile memory that can be erased and reprogrammed ± Magnetic tape ± Magnetic Disk ± CD and DVD ² Systems ± RAID ± File systems ± DBMS (Data Base management Systems)
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4 Attributes of the storage medium/system ± Durability Î the time it remembers ± Stability Î whether or not the data is changed during the storage ± Persistence Î property of data storage system, it keeps trying to preserve the data
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5 Critical properties of a storage medium/system ± Read/Write Coherence Î the result of a READ of a memory cell should be the same as the most recent WRITE to that cell. ± Before-or-after atomicity Î the result of every READ or WRITE is as if that READ or WRITE occurred either completely before or completely after any other READ or WRITE
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6 time WRITE item A in cell M A M READ from cell M A M A A Current READ/WRITE Previous READ/WRITE Next READ/WRITE
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7 hy it is hard to guarantee the critical properties? ± Concurrency Î multiple threads could READ/WRITE to the same cell ± Remote storage Î The delay to reach the physical storage may not guarantee FIFO operation ± Optimizations Î data may be buffered to increase I/O efficiency ± Cell size may be different than data size Î data may be written to multiple cells. ± Replicated storage Î difficult to maintain consistency.
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8 Access type; access time ± Sequential access ² Tapes ² CD/DVD ± Random access devices ² Disk ± Seek ± Search time ± Read/Write time ² RAM
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9 Physical memory organization ± RAM Î two dimensional array. To select a flip-flop provide the x and y coordinates. ± Tapes Î blocks of a given length and gaps (special combination of bits. ± Disk: ² Multiple platters ² Cylinders correspond to a particular position of the moving arm ² Track Î circular pattern of bits on a given platter and cylinder ² Record Î multiple records on a track
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10 Names and physical addresses ± Location addressed memory Î the hardware maps the physical coordinates to consecutive integers, addresses ± Associative memory Î unrestricted mapping; the hardware does not impose any constraints in mapping the physical coordinates Figure 2.2 from textrbook
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11 RAID – Redundant Array of Inexpensive Disks ± The abstraction put to work to increase performance and durability.
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Lecture3 - COT 5611 Operating Systems Design Principles...

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