Course Code: CS 4001 (Same as CB/IT 4001)
Course Title: Operating Systems
Author: Garima Kanwar (BTER Polytechnic Classes)
Blog: Rajasthan Polytechnic
(Course Code: CS 4001 / CB/IT 4001 – Operating Systems – 4th Semester Polytechnic CS)
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3.1 File Management
3.1.1 Concept of a File
A file is a collection of data stored on a storage device. It is the fundamental unit of storage in a computer system. Files can contain text, images, videos, or executable programs.
Types of Files
Text Files (.txt, .doc, .pdf) - Contain plain text or formatted text.
Binary Files (.exe, .bin) - Contain machine-readable data.
Multimedia Files (.jpg, .mp3, .mp4) - Store images, audio, and video.
System Files (.sys, .dll) - Used by the operating system.
File Attributes
Each file has the following attributes:
Name: Identifies the file.
Type: Determines the file format.
Size: Defines the file’s storage capacity.
Location: Specifies where the file is stored.
Protection: Controls file access permissions.
File Operations
The operating system supports the following file operations:
✅ Create - Making a new file.
✅ Open - Accessing an existing file.
✅ Read - Retrieving data from a file.
✅ Write - Adding or modifying data in a file.
✅ Close - Ending file access.
✅ Delete - Removing a file permanently.
(Diagram: File operations and attributes overview)
3.1.2 Access Methods
A file can be accessed in different ways depending on how the data is stored and retrieved.
1. Sequential Access
📌 Data is read in a linear manner, from start to end.
📌 Used in text files and log files.
2. Direct (Random) Access
📌 Allows access to any part of the file without reading previous data.
📌 Used in databases and executable files.
3. Indexed Access
📌 Uses an index to locate data blocks quickly.
📌 Similar to an index in a book.
(Diagram: Comparison of access methods)
3.2 Directory Structure
A directory is a file system structure that stores files and other directories.
Types of Directory Structures
📂 Single-Level Directory - All files stored in one directory. ❌ Not suitable for large systems.
📂 Two-Level Directory - Separate directories for each user.
📂 Tree-Structured Directory - Hierarchical structure like folders in Windows.
📂 Acyclic Graph Directory - Supports shared files and links.
📂 General Graph Directory - Allows multiple parent directories, making it complex.
(Diagram: Different directory structures)
3.3 File System Structure and Implementation
3.3.1 Directory Implementation
A directory can be implemented using:
✔ Linear List: Stores files sequentially (Simple but slow).
✔ Hash Table: Uses a hashing function for faster searching.
3.3.2 Free-Space Management
The operating system manages unused disk space using:
📌 Bit Vector - Uses bits (0 for free, 1 for occupied).
📌 Linked List - Free blocks linked together.
📌 Grouping - Stores free blocks in groups.
📌 Counting - Stores starting address and number of blocks.
3.3.3 Efficiency and Performance
To enhance efficiency, OS uses:
✅ Disk Caching - Stores frequently used data.
✅ Defragmentation - Reduces scattered file storage.
✅ File Allocation Methods - Helps in space management.
(Diagram: File system implementation techniques)
3.4 Different Types of File Systems
| File System | Description | Example |
|---|---|---|
| FAT32 | Simple, used in USB drives | Windows |
| NTFS | Advanced security & compression | Windows |
| ext3/ext4 | Journaling system | Linux |
| HFS+ | Used in macOS | Mac |
| exFAT | Used for large external drives | Windows, Mac |
(Diagram: Comparison of different file systems)
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