The document provides an overview of file concepts, including file attributes, types, access methods, and directory structures. It discusses file system mounting, sharing, protection, directory implementation, allocation methods, and free-space management. Key topics include sequential and random access methods, various directory structures, and access control mechanisms for protecting files.

1. 1. File Concepts
A file is a collection of related information stored on secondary storage. It has attributes such as:
 Name: Human-readable identifier.
 Type: Format (e.g., .txt, .exe, .jpg).
 Location: Address on storage.
 Size: Current file size in bytes.
 Protection: Permissions (read/write/execute).
 Time, date, and user information: Metadata for security and tracking.
File Types
 Regular Files: User data (text, binary, multimedia, etc.).
 Directories: Contain file and directory entries.
 Special Files: System-related files (device drivers, pipes, etc.).
2. Access Methods
Different ways to read/write files:
1. Sequential Access
o Data is read in order.
o Common in text files.
2. Direct (Random) Access
o Jump to any part of the file.
o Used in databases and executable files.
3. Indexed Access
o Index table stores pointers to file blocks.
o Efficient for large files with random access needs.

2. 3. Directory and Disk Structure
The directory structure organizes files on disk.
Directory Structures
1. Single-Level Directory
o Simple but all files are in one directory, leading to name conflicts.
2. Two-Level Directory
o Separate directories for each user.
3. Tree-Structured Directory
o Hierarchical structure with subdirectories.
4. Acyclic Graph Directory
o Allows shared directories.
5. General Graph Directory
o Allows cycles (must handle links carefully).
Disk Structure
 Boot Block: Contains boot loader.
 Superblock: Holds file system metadata.
 File Control Block (FCB): Stores file details.
 Data Blocks: Hold file content.
4. File System Mounting
 A file system must be mounted before use.
 Mount Point: Directory where another file system is attached.
 Ensures proper access permissions and consistency.

3. 5. File Sharing
Types of File Sharing
 Local Sharing: Among users on the same system.
 Remote Sharing: Across networks (NFS, SMB).
 Access Control: Permissions define who can read/write.
File Locking
 Shared Lock: Multiple processes can read.
 Exclusive Lock: Only one process can write.
6. Protection
Prevents unauthorized access to files.
Access Control Methods
1. Access Control Lists (ACLs)
o Lists users/groups with specific permissions.
2. Unix-style Protection Bits
o Owner-Group-World permissions (rwxr-x--x).
3. Role-Based Access Control (RBAC)
o Access based on user roles.
7. Directory Implementation

4. Data Structures for Directories
1. Linear List
o Simple but slow searching.
2. Hash Table
o Faster lookup but more complex management.
8. Allocation Methods
Determines how files are stored on disk.
1. Contiguous Allocation
o Files occupy consecutive blocks.
o Fast but causes fragmentation.
2. Linked Allocation
o Each file block points to the next.
o No fragmentation, but slow access.
3. Indexed Allocation
o Index block holds pointers to file blocks.
o Fast random access.
9. Free-Space Management
Manages available disk space.
1. Bit Vector
o Bitmap indicating free/used blocks.
2. Linked List
o Free blocks linked together.

5. 3. Grouping
o Lists free blocks in groups for efficiency.
4. Counting
o Stores contiguous free block count.