Please enable JavaScript.

Coggle requires JavaScript to display documents.

TOPIC 3: FILE MANAGEMENT - Coggle Diagram

- - - - WHY?
        
        The flexibility to access records in any order without the hassle of searching from the beginning of the file.
        
        Relative addresses are given to records for identification.
        
        When records are received and stored, logical addresses are computed.
        
        Hashing algorithms are used.
        
        it uses direct access files which can be implemented only on direct access storage devices.
        
        ADVANTAGE
        
        Fast access to records. Records can be quickly rewritten to original addresses after modification. Therefore, It can be updated quickly
        
        Can be accessed sequentially, by starting at first relative address and incrementing it by one to get to the next record.
        
        No need to preserve order of the records, can be added or deleted quickly.
        
        DISADVANTAGE
        
        Several records with unique keys may generate the same logical addresses (collision).
- - - - Definition
        
        A collection of nodes containing information about all files
        
        Both the directory structure and the files reside on disk
        
        Backups of these two structures are kept on tapes
      - A Typical File-system Organization
      - A disk (or any storage device that is large enough) can be used in its entirety for a file system.
        
        It is also desirable to place multiple file systems on a disk such as swap space or unformatted (raw) disk space.
        
        These parts are known variously as partitions, slices, or minidisks (IBM).
        
        A file system can be created on each of these parts of the disk. The parts can also be combined to form larger structures known as volumes and file systems can be created on these as well.
        
        VOLUMES
        
        We refer to a chunk of storage that holds a file system
        
        Each of it can be thought of as a virtual disk
        
        store multiple operating systems, allowing a system to boot and run more than one.
        
        Each volume that contains a file system must also contain information about the files in the system
        
        This information is kept in entries in a device directory or volume table of contents
        
        records information—such as name, location, size, and type—for all files on that volume.
        
        This information is kept in entries in a device directory or volume table of contents.
        
        records information—such as name, location, size, and type—for all files on that volume.
      - Example
        
        Both the directory structure and the files reside on disk
        
        Backups of these two structures are kept on tapes
    - - DEFINITION
        
        can be viewed as a symbol table that translates file names into their directory entries
      - Operations Performed on Directory
        
        Search for a file
        
        Create a file
        
        Delete a file
        
        List a directory
        
        Rename a file
        
        Traverse the file system
    - - Definition
        
        The simplest directory structure
        
        All files are contained in the same directory, which is easy to support and understand
        
        has significant limitations, however, when the number of files increases or when the system has more than one user
      - Even a single user may find it difficult to remember the names of all the files as the number of files increases.
        
        It is not uncommon for a user to have hundreds of files on one computer system
        
        an equal number of additional files on another system.
        
        Keeping track of so many files is a daunting task.
    - - A single-level directory often leads to confusion of file names among different users
        
        The standard solution is to create a separate directory for each user
        
        Each user has his own user file directory (LTD)
        
        The UFDs have similar structures, but each lists only the files of a single user
        
        When a user job starts or a user logs in, the system's master file directory (MFD) is searched
        
        The MFD is indexed by user name or account number
        
        each entry points to the UFD for that user
      - Separate directory for each user
        
        Path name
        
        Can have the same file name for different user
        
        Efficient searching
        
        No grouping capability
- - - - A file has a certain defined structure, which depends on its type.
        
        File Structure
        
        :check: A text file is a sequence of characters organized into lines (and possibly pages).
        :check: A source file is a sequence of subroutines and functions, each of which is further organized as declarations followed by executable statements.
        :check: An object file is a sequence of bytes organized into blocks understandable by the system's linker.
        :check: An executable file is a series of code sections that the loader can bring into memory and execute.
  - - - Some systems differentiate between uppercase and lowercase characters in names, whereas other systems do not.
      - A file's attributes usually consist of these:
        
        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
  - - - :star: It is the operating system that enable files to be read or run by a computer.
        :star: If an operating system recognizes the type of a file, it can then operate on the file in reasonable ways.
        :star: A common technique for implementing file types is to include the type as part of the file name. The name is split into two parts—a name and an extension, usually separated by a period character. The user and the operating system can tell from the name alone what the type of a file is.
- - - - Read operation ( read next )
        
        Read the next portion of the file and automatically advances a file pointer, which tracks the I/O location.
      - Write operation ( write next )
        
        Appends to the end of the file and advances to the end of newly written material ( the new end of file )