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Chapter 11: File-System Interface
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File Concept and Attributes
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A **file** is a named collection of related information stored on secondary storage.
Operating systems abstract physical storage into logical files.

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

Directory Operations
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- Search for a file.
- Create/delete files or subdirectories.
- List directory contents.
- Rename files.
- Traverse the directory tree.

Directory Organization Schemes
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- **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.