Chapter12-OS7e - Operating Systems: Internals and Design...

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Chapter 12 File Management Seventh Edition By William Stallings Operating  Systems: Internals  and  Design  Principles
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Operating Systems: Operating Systems: Internals and Design Principles Internals and Design Principles If there is one singular characteristic that makes squirrels unique  among small mammals it is their natural instinct to hoard food.  Squirrels have developed sophisticated capabilities in their hoarding.  Different types of food are stored in different ways to maintain quality.  Mushrooms, for instance, are usually dried before storing. This is done  by impaling them on branches or leaving them in the forks of trees for  later retrieval. Pine cones, on the other hand, are often harvested while  green and cached in damp conditions that keep seeds from ripening.  Gray squirrels usually strip outer husks from walnuts before storing. SQUIRRELS: A WILDLIFE HANDBOOK, Kim Long
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Files Files Data collections created by users The File System is one of the most important parts of the OS to a user Desirable properties of files:
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File Systems File Systems Provide a means to store data organized as files as well as a collection of  functions that can be performed on files Maintain a set of attributes associated with the file Typical operations include: Create Delete Open Close Read Write
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File Structure File Structure
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File Structure  Files can be structured as a collection of records or as a  sequence of bytes UNIX, Linux, Windows, Mac OS’s consider files as a  sequence of bytes Other OS’s, notably many IBM mainframes, adopt the  collection-of-records approach; useful for DB COBOL supports the collection-of-records file and can  implement it even on systems that don’t provide such files  natively.
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Structure Terms Structure Terms Field basic element of data contains a single value fixed or variable length File collection of related fields that can  be treated as a unit by some  application program One field is the  key  – a unique  identifier Record Database collection of similar records treated as a single entity may be referenced by name access control restrictions  usually apply at the file level collection of related data relationships among elements  of data are explicit  designed for use by a number  of different applications consists of one or more types  of files
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File Management System  File Management System  Objectives Objectives Meet the data management needs of the user Guarantee that the data in the file are valid Optimize performance Provide I/O support for a variety of storage device types
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Chapter12-OS7e - Operating Systems: Internals and Design...

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