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L10-FileManagement

L10-FileManagement - File Management CSIS0230A Lecture Ten...

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File Management CSIS0230A Lecture Ten Concepts File allocation strategies Free space management
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Recommended Reading Chapter 13 of Operating Systems, 3rd edition by Deitel et. al exclude sections 13.5, 13.11-13.12 2 CSIS0230A Principles of Operating Systems
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References Chapter 13 of Operating Systems, 3rd edition by Deitel et. al Chapter 10 and 11 of Operating System Principles, 7th edition by Silberschatz et. Al Chapter 12 of Operating Systems Internal and Design Principles, 6th edition by William Stallings 3 CSIS0230A Principles of Operating Systems
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File Concept What is a file? A uniform logical view of information storage that is manipulated as a unit A named collection of related information that is recorded on secondary storage File is mapped by the OS onto physical devices Has a certain defined structure, which depends on its type text file a sequence of characters organized into lines 4 CSIS0230A Principles of Operating Systems
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File Attributes File characteristics include: Name only information kept in human-readable form Identifier unique tag identifies file within file system Type needed for systems that support different types Location pointer to file location on device Size current file size Accessibility controls who can do Rr, Wr, Ex Time, date, and user identification data for protection, security, and usage monitoring Info about files are kept in the directory structure, which is maintained on the disk so is also a file 5 CSIS0230A Principles of Operating Systems
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File Operations File is an abstract data type Open associate the target file to the process, allowing the process to perform functions on the file Close process no longer perform functions on the file until it is reopened Create a new file is defined (space is allocated) and an entry must be made in the directory Delete release all file space and erase the directory entry Write make updates to the file according to the current pointer Read copy data (starting from location points by the current pointer) from a file to the memory Seek reposition the current pointer to a given value 6 CSIS0230A Principles of Operating Systems
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File Systems A file system organizes files and manages access File Management Providing services to users and applications in the use of files Storage management Allocating space for files on storage devices Should exhibit device independence Users should be able to refer to their files by symbolic names rather than having to use physical device names and physical location File integrity Should also provide backup and recovery capabilities to prevent either accidental loss or malicious destruction of information May also provide encryption and decryption capabilities to make information useful only to its intended audience 7 CSIS0230A Principles of Operating Systems
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