CDFS (CD-ROM File System)
CDFS, or the CD-ROM File System, is a generic term often used to refer to file systems designed for optical disc media, particularly ISO 9660 and its extensions. It allows operating systems to read and manage data on CDs and is widely supported across platforms. Here's a detailed look at CDFS and its features:
Structure of the CDFS File System
1. Volume Descriptor:
The volume descriptor contains metadata about the file system:
Volume Identifier:The name of the volume as displayed to the user.
Volume Space Size:Total number of logical blocks in the file system.
Logical Block Size:Typically 2048 bytes, optimized for optical discs.
Root Directory Record:Points to the root directory of the file system.
2. File Structure:
CDFS organizes files and directories hierarchically:
Root Directory:
The starting point for all files and directories.
File Entries:
Metadata for files, including size, location, and attributes.
Path Table:
Provides a quick lookup mechanism for directory paths.
3. File Naming:
CDFS supports strict naming conventions, which vary based on the standard used:
ISO 9660 Level 1:
File names are limited to 8 characters, a period, and a 3-character extension (e.g.,
FILE.TXT).
ISO 9660 Level 2:
Allows file names up to 31 characters.
Joliet Extension:
Supports Unicode and longer file names.
4. Multi-Session Support:
CDFS supports multi-session discs, enabling incremental writing of data:
Session Tracking:
Each session appends data while retaining previous sessions.
Cross-Platform Compatibility:
Ensures data is accessible on various operating systems.
Features of CDFS
Cross-Platform Compatibility:
Supported by virtually all modern operating systems.
Hierarchical Structure:
Organizes files and directories for easy navigation.
Read-Only Access:
Primarily designed for read-only media like CDs.
Extensions:
Enhancements like Joliet and Rock Ridge add functionality.
Efficient Storage:
Optimized for the block size of optical media.
Limitations of CDFS
File Name Restrictions:
Limited file name length and character set without extensions.
Read-Only Nature:
Not designed for writable media, though extensions like UDF address this.
Limited Scalability:
Primarily for smaller volumes typical of CD-ROMs.
Tools and Commands for CDFS
mkisofs:Creates an ISO 9660 file system image.
mount:Mounts a CDFS volume for access.
isoinfo:Displays information about ISO 9660 images.
dd:Copies ISO images to storage devices.
Example Usage
CDFS remains a fundamental standard for optical media, providing a reliable and widely supported way to store and distribute data. Its extensions, such as Joliet and Rock Ridge, ensure compatibility with modern needs while retaining its foundational simplicity.