#18 File Organization

#18 File Organization - File Organizations File Part I Part...

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File Organizations File Organizations
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Part I Part I File-System Interface File-System Interface
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File Concept File Concept Contiguous logical address space Types: Data numeric character binary Program
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File Concept File Concept The file system is the most visible aspect of an operating system. (for most users) - files store data and programs - the operating system implements the abstract concept of a file by managing mass storage devices, such as tapes and disks - files are normally organized into directories to ease their use
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File Concept File Concept File management - one of the most visible services of an operating system - computers can store information in several different physical forms; magnetic tape, disk, and are the most common forms
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File Structure File Structure None - sequence of words, bytes Simple record structure Lines Fixed length Variable length Complex Structures Formatted document Relocatable load file Who decides: Operating system Program
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File Definition File Definition A file is a collection of related information defined by its creator. - files represent programs (both source and object forms) and data - data files may be numeric, alphabetic or alphanumeric - files may be free form, such as text files, or may be rigidly formatted - in general, a file is a sequence of bits, bytes, lines or records whose meaning is defined by its creator and user
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File Attributes File Attributes Name – only information kept in human-readable form Identifier – unique tag (number) identifies file within file system Type – needed for systems that support different types Location – pointer to file location on device Size – current file size Protection – controls who can do reading, writing, executing Time, date, and user identification – data for protection, security, and usage monitoring Information about files are kept in the directory structure, which is maintained on the disk
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File Definitions File Definitions The information in a file is defined by its creator. - many different types of information may be stored in a file: source programs, object programs, numeric data, text, payroll records, etc. A file has a certain defined structure according to its use. a. text file is a sequence of characters organized into lines (and possibly pages) b. source file is a sequence of subroutines and functions, each of which is further organized as declarations followed by executable statement c. object file is a sequence of words organized into loader record blocks
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Files on Disks Files on Disks Files are usually kept on disks. - disk systems typically have a well defined block size determined by the size of a sector - all disk I/O is in units of one block (physical record), and all blocks are the same size - it is unlikely that the physical record size will exactly match the length of the desired logical record -logical records may even vary in length - packing a number of logical records into physical blocks is a common solution to this problem
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#18 File Organization - File Organizations File Part I Part...

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