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A part of a lecture series on Operating Systems at the University of Bedfordshire. It focuses on file management, covering topics such as interaction with the file manager, files, physical storage allocation, directories, file system, access, and data compression.
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Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction 4 Interaction with the file manager Files Physical storage allocation Directories File system Access Data compression summary
Operating Systems
1 Keep track of where each file is stored 2 Use a policy that will determine where and how the files will be stored, making sure to efficiently use the available storage space and provide efficient access to the files. 3 Allocate each file when a user has been cleared for access to it, and then record its use. 4 Deallocate the file when the file is to be returned to storage, and communicate its availability to others who may be waiting for it.
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction 5 Interaction with the file manager Files Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the 7 file manager Files Physical storage allocation Directories File system Access Data compression summary
Operating Systems
embedded commands are: OPEN / CLOSE - pertain to the availability of a file for the program invoking it. READ / WRITE - are I/O commands. (^) MODIFY - specialised WRITE command for existing data files, allows for appending records or for rewriting selected records in their origional place in the file. interactive commands are: (^) CREATE / DELETE - deal with the system’s knowledge of the file (some systems have the first instance of SAVE command, others OPEN NEW, OPEN... FOR OUTPUT. RENAME - allows users to change the name of an existing file. COPY - lets users make duplicate copies of existing files.
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the 8 file manager Files Physical storage allocation Directories File system Access Data compression summary
Operating Systems
1 Move the read/write heads of the cylinder where the record is to be found. 2 Wait for the rotational delay until the sector containing the desired record passes under the read/write head. 3 Activate the appropriate read/write head and read the record. 4 Transfer the record to main memory. 5 Send a flag to indicate that the device is free to satisfy another request.
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 10 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 11 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Name – only information kept in human-readable form. Identifier – non-human readable unique tag (usually a number). 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.
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 13 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
helps prevent user mistakes convenient by automatically doing various jobs after a command must define every file type allowed and difficult to create new file types
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 14 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
1 relative filename 2 extension (called a suffix in UNIX/Linux)
MS-DOS - allows names from one to eight alphanumeric characters, but without spaces most modern operating systems do not have restrictions on filenames.
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 16 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Easiest File searched from its beginning until record is found
(^) Only on direct access storage devices (^) Records identified by their relative address to the beginning of the file
(^) Combines the best of sequential and direct access
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files 17 Physical storage allocation Directories File system Access Data compression summary
Operating Systems
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files Physical storage 19 allocation Directories File system Access Data compression summary
Operating Systems
records stored one after another any record can be found and read by knowing its starting address and size ease of direct access, every part of the file is stored in the same compact area file cant be expanded unless there is empty space immediately following it - also causing fragmentation
Lecture #5 File Management David Goodwin University of Bedfordshire
Introduction Interaction with the file manager Files Physical storage 20 allocation Directories File system Access Data compression summary
Operating Systems
(^) files use any space available on disk (^) records stored in a contigious manner only if there’s enough empty space (^) any remaining records, and all other additions to the file, are stored in other sections of the disk sometimes called extents of the file - linked together with pointers in one of two ways (^) at storage level - each extent points to the next one in sequence (^) at directory level - each extent is listed with its physical address, size, and a pointer to the next extent. A null pointer indicates it’s the last one. (^) doesnt support direct access
