File Management Overview

File Management Overview

• File Manager is the software responsible for creating, deleting, modifying, and controlling file access. It also supports libraries of programs for online users, spooling, and interactive computing.

File Concept

• Files are the fundamental building blocks of operating systems, storing information and data permanently.
• Operating systems don't care about the contents within files; they map files to physical devices.
• A program (file) represents a program and its data; the output of a program is an executable file.

File Access Methods

• File access mechanisms define how records within a file are accessed.
• Sequential access involves accessing records in order, from the beginning to the end.
  • Advantages: simple and easy to implement.
  • Disadvantages: slow and inefficient for random access, especially with large files.
• Direct access (random access) allows direct access to any record within the file without processing preceding records.
  • Advantages: speed and efficiency in random access
  • Disadvantages: more complex and difficult to implement than sequential access.
• Indexed access combines sequential and direct access through an index file mapping logical keys to physical addresses.
  • Advantages: speed and efficiency for both random and sequential access.
  • Disadvantages: requires additional storage for the index, increasing system complexity and cost.

File Types

• File types allow operating systems to distinguish between different file types (text, source, binary, etc.).
• Many operating systems support diverse file types.
  • Ordinary files hold user information (text, databases, programs).
  • Directory files list files and related information (equivalent to "folders").
  • Special files represent physical devices (disks, terminals, printers).
    • Character special files handle data character-by-character (terminals, printers).
    • Block special files handle data in blocks (disks, tapes).

File Operations

• Create: Generates an empty file.
• Delete: Removes a file, freeing up disk space.
• Open: Prepares a file for use.
• Close: Releases resources associated with a file.
• Read: Retrieves data from a file.
• Write: Writes data to a file, typically at the current position.
• Append: Adds data to the end of a file.
• Seek: Positions the file pointer to a specific location.
• Rename: Changes a file's name.

Directory Structure

• Directories list files, containing information like file names, types, sizes, ownership, permissions, and timestamps.
• Types:
  • Single-level: All files in one directory.
  • Two-level: A master directory containing subdirectories.
  • Tree-structured: Directories can contain files and subdirectories, creating a hierarchical structure.

File Management System Structure

• Layered file systems organize the interaction between application programs and devices using multiple layers: application program, logical file system, file organization module, basic file system, I/O control interface, and physical hardware.

Data Compression

• Data compression reduces the amount of bits required to represent data, saving storage capacity, speeding up file transfer, and lowering costs for hardware and network bandwidth.
• Compression algorithms determine how data can be shrunk.
• When transferring data over the internet, files are often compressed (e.g., ZIP, GZIP) for efficient transmission.