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Chapter 10: File-System, ACM Shows the access rights for each user for…

- - - - Volume contains a file system and informations
      - Device directory is also known as volume table of contents
      - Typical Volume Configuration
        
        Secondary storage unit (removable/non-removable)
        
        Multi-file volume -contains many files
        
        Multi-volume files : large files spread across volumes
        
        Volume name : written by file manager on each unit
  - - - MFD
        
        Names and characteristics of files in volume
        
        Subdirectories
        
        Single-Level directory
        
        for all users
        
        single directory per volume
        
        supported by early OS
        
        Disadvantages:
        
        Long search time for individual file.
        
        Users cannot create subdirectories.
        
        Users cannot safeguard their files because entire directory
        
        was freely available to every user.
        
        Each program needs unique name
        
        Two-Level directory
        
        separate directory for each user
        
        Advantages:
        
        Path name.
        
        Can have the same file name for different user.
        
        Efficient searching
        
        Disadvantages
        
        Problem remain ->
        No logically file grouping
        capability
        
        Tree-Structure directory
        
         File managers today.
        
         Users create own subdirectories (folders).
        
         Related files are grouped together.
        
         Implemented as upside-down tree.
        
         Efficient system searching of individual directories.
        
         May require several directories to reach file
        
        Advantages:
        -Efficient searching.
        -Grouping Capability
        
        Path name
        
        can be divided into absolute or relative
        
        Delete a file: rm <file-name>
        
        Create a new subdirectory: mkdir <dir-name>
        
        Relative path name:
        -Current directory: root/spell/mail
        -Relative path: prt / first
        
        Remainder of volume
  - - - Links
        
        implemeted as
        
        absolute
        
        relative
        
        the name of the real file is included in the link information
      - Deletion
        
        dict/count is deleted
        
        dangling pointer
        
        solution
        
        Backpointers : delete all pointers
        
        Backpointers using a saisy-chain organization
        
        Entry-hold-count solution
  - - - allow only links to file not subdirectories
      - Garbage collection
      - use a cycle detection algorithm