Chapter 11: File-System Interface

File Concept and Attributes

A file is a named collection of related information stored on secondary storage. Operating systems abstract physical storage into logical files.

File Attributes

Common attributes stored in a file’s metadata include:

  • Name – Human-readable identifier.

  • Identifier – Unique internal tag (numeric or handle).

  • Type – Indicates format (text, binary, executable).

  • Location – Pointer to file location(s) on disk.

  • Size – Current file size.

  • Protection – Access permissions (read/write/execute).

  • Timestamps – Creation, last modified, last accessed.

  • Owner / Group – Security and accountability.

These attributes are stored in system structures such as FCBs (File Control Blocks) or inodes.

File Operations

OS provides system calls to manipulate files:

  • Create() Allocates space for metadata; establishes a new directory entry.

  • Open() Loads metadata into memory; returns a file handle.

  • Close() Writes metadata back to disk; releases handle.

  • Read() Transfers data from file to memory buffer.

  • Write() Updates content and may expand file size.

  • Seek() Moves file pointer to a specific location.

  • Delete() Removes directory entry and releases storage blocks.

  • Truncate() Deletes file contents but keeps attributes intact.

The OS tracks file positions and permissions with open-file tables.

Directory Structure

A directory contains file names and pointers to file metadata. It provides a user-friendly organizational hierarchy.

Directory Operations

  • Search for a file.

  • Create/delete files or subdirectories.

  • List directory contents.

  • Rename files.

  • Traverse the directory tree.

Directory Organization Schemes

  • Single-Level Directory Simple but causes name conflicts.

  • Two-Level Directory Separate directory per user.

  • Tree-Structured Directory Hierarchical folders; supports pathnames.

  • Acyclic-Graph Directory Allows shared subdirectories or files via links.

  • General Graph Directory Allows cycles; requires careful traversal.