ISO (ISO 9660 Optical Disc Image)

Overview

ISO is a disc image file format that contains an exact copy of data from an optical disc, such as a CD, DVD, or Blu-ray. The format follows the ISO 9660 standard for optical disc file systems, making it a universal format for distributing software, operating systems, and large datasets while preserving the original disc structure and boot capability.

Technical Details

File System Standards

• ISO 9660: Base standard for CD-ROM file systems
• Joliet: Microsoft extension for long filenames and Unicode
• Rock Ridge: POSIX extension for Unix-like systems
• UDF (Universal Disk Format): Modern standard for DVDs and Blu-rays

Structure Components

• Boot Record: Information for bootable discs
• Primary Volume Descriptor: File system metadata
• Directory Records: File and folder structure
• Path Tables: Directory hierarchy optimization
• File Data: Actual file contents

Size Limitations

• ISO 9660 Level 1: 8.3 filenames, 8 directory levels
• ISO 9660 Level 2: 31 character filenames
• ISO 9660 Level 3: Files larger than 4GB supported
• Maximum Size: 8TB for modern implementations

History and Development

The ISO format originated from the ISO 9660 standard published in 1988, which defined the file system for CD-ROM media. It was designed to ensure cross-platform compatibility and became the foundation for optical disc storage. The format has evolved to support various extensions and larger media types while maintaining backward compatibility.

Code Examples

Creating ISO Files

Linux/macOS (mkisofs/genisoimage)

# Create basic ISO from directory
mkisofs -o output.iso -R -J -T /path/to/source/directory

# Create bootable ISO (for Linux distributions)
mkisofs -o bootable.iso -b isolinux/isolinux.bin -c isolinux/boot.cat \
        -no-emul-boot -boot-load-size 4 -boot-info-table -R -J -T /source

# Create ISO with volume label
mkisofs -o labeled.iso -V "My Volume Label" -R -J /source/directory

# Create ISO excluding certain files
mkisofs -o filtered.iso -R -J -T -m "*.tmp" -m "*.log" /source

Windows (using PowerShell)

# Using DISM (Windows 10/11)
$source = "C:\Source\Directory"
$destination = "C:\Output\image.iso"

# Create ISO using Windows API
Add-Type -AssemblyName System.IO.Compression.FileSystem
$imapi = New-Object -ComObject IMAPI2.MsftDiscMaster2
$recorder = New-Object -ComObject IMAPI2.MsftDiscRecorder2
$fileSystemImage = New-Object -ComObject IMAPI2.MsftFileSystemImage

$fileSystemImage.VolumeName = "MyVolume"
$fileSystemImage.Root.AddTree($source, $false)

$resultImage = $fileSystemImage.CreateResultImage()
$stream = $resultImage.ImageStream

# Save to file
$buffer = New-Object byte[] 1024
$file = [System.IO.File]::Create($destination)
do {
    $bytesRead = $stream.Read($buffer, 0, $buffer.Length)
    $file.Write($buffer, 0, $bytesRead)
} while ($bytesRead -gt 0)

$file.Close()
$stream.Close()

Mounting and Extracting ISOs

Linux

# Mount ISO file
sudo mkdir /mnt/iso
sudo mount -o loop image.iso /mnt/iso

# Extract ISO contents
7z x image.iso -o/destination/directory
# or
bsdtar -xf image.iso -C /destination/directory

# Unmount ISO
sudo umount /mnt/iso

Python ISO Manipulation

import pycdlib
import os

class ISOManager:
    def __init__(self):
        self.iso = pycdlib.PyCdlib()
    
    def create_iso(self, source_dir, output_file, volume_label="DISC"):
        """Create ISO from directory"""
        self.iso.new(interchange_level=1)
        self.iso.add_directory('/BOOT')
        
        # Walk through source directory
        for root, dirs, files in os.walk(source_dir):
            # Add directories
            for dir_name in dirs:
                local_path = os.path.join(root, dir_name)
                iso_path = '/' + os.path.relpath(local_path, source_dir).replace(os.sep, '/').upper()
                self.iso.add_directory(iso_path)
            
            # Add files
            for file_name in files:
                local_path = os.path.join(root, file_name)
                iso_path = '/' + os.path.relpath(local_path, source_dir).replace(os.sep, '/').upper()
                self.iso.add_file(local_path, file_identifier=iso_path)
        
        # Write ISO
        self.iso.write(output_file)
        self.iso.close()
    
    def extract_iso(self, iso_file, output_dir):
        """Extract ISO contents"""
        self.iso.open(iso_file)
        
        # Create output directory
        os.makedirs(output_dir, exist_ok=True)
        
        # Extract all files
        for child in self.iso.list_children('/'):
            if child.is_file():
                output_path = os.path.join(output_dir, child.file_identifier().decode('utf-8'))
                self.iso.get_file_from_iso(fp=open(output_path, 'wb'), 
                                          file_identifier=child.file_identifier())
        
        self.iso.close()
    
    def get_iso_info(self, iso_file):
        """Get ISO metadata"""
        self.iso.open(iso_file)
        
        pvd = self.iso.pvd
        info = {
            'volume_identifier': pvd.volume_identifier.decode('utf-8').strip(),
            'system_identifier': pvd.system_identifier.decode('utf-8').strip(),
            'volume_size': pvd.space_size,
            'creation_date': str(pvd.volume_creation_date),
            'modification_date': str(pvd.volume_modification_date)
        }
        
        self.iso.close()
        return info

# Usage
iso_manager = ISOManager()

# Create ISO
iso_manager.create_iso('/path/to/source', 'output.iso', 'MY_DISC')

# Extract ISO
iso_manager.extract_iso('input.iso', '/path/to/extract')

# Get ISO information
info = iso_manager.get_iso_info('input.iso')
print(f"Volume: {info['volume_identifier']}")
print(f"Size: {info['volume_size']} sectors")

Common Use Cases

Software Distribution

• Operating System Images: Linux distributions, Windows installers
• Application Software: Large software packages and suites
• Driver Collections: Hardware driver packages
• Antivirus Rescue Discs: Bootable security tools

Backup and Archival

• System Backups: Complete system state preservation
• Data Archives: Long-term data storage and preservation
• Document Collections: Large document repositories
• Media Libraries: Video and audio collections

Virtualization

• Virtual Machine Installation: OS installation media
• Container Base Images: System templates
• Emulation: Classic software and games
• Testing Environments: Isolated system testing

Development and Testing

• Build Artifacts: Software release packages
• Test Data Sets: Large testing datasets
• Documentation: Technical documentation bundles
• Development Tools: Portable development environments

Tools and Software

Creation Tools

• ImgBurn: Windows disc burning and ISO creation
• Brasero: Linux CD/DVD burning software
• K3b: KDE disc burning application
• InfraRecorder: Open-source Windows burning tool

Command Line Tools

• mkisofs/genisoimage: Unix ISO creation utility
• cdrtools: Comprehensive disc authoring suite
• xorriso: Portable ISO creation and manipulation
• 7-Zip: Archive manager with ISO support

Virtual Drive Software

• VirtualCloneDrive: Windows virtual drive mounting
• WinCDEmu: Open-source virtual drive emulator
• DAEMON Tools: Commercial virtual drive software
• PowerISO: Comprehensive disc image utility

Programming Libraries

• pycdlib: Python ISO manipulation library
• libisofs: C library for ISO creation
• libisoburn: C library for optical media
• IMAPI2: Windows Imaging API

Bootable ISO Creation

BIOS Boot (Legacy)

# Create bootable ISO with ISOLINUX
mkisofs -o bootable.iso \
        -b isolinux/isolinux.bin \
        -c isolinux/boot.cat \
        -no-emul-boot \
        -boot-load-size 4 \
        -boot-info-table \
        -R -J -T \
        /source/directory

UEFI Boot (Modern)

# Create hybrid BIOS/UEFI bootable ISO
xorriso -as mkisofs \
        -o bootable.iso \
        -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin \
        -c isolinux/boot.cat \
        -b isolinux/isolinux.bin \
        -no-emul-boot \
        -boot-load-size 4 \
        -boot-info-table \
        -eltorito-alt-boot \
        -e EFI/boot/efiboot.img \
        -no-emul-boot \
        -isohybrid-gpt-basdat \
        /source/directory

File System Extensions

Joliet Extension

• Long Filenames: Up to 64 characters
• Unicode Support: International character sets
• Windows Compatibility: Enhanced Windows support

Rock Ridge Extension

• POSIX Attributes: File permissions and ownership
• Symbolic Links: Unix-style symbolic links
• Long Filenames: Up to 255 characters
• Case Sensitivity: Preserves case information

UDF (Universal Disk Format)

• Large Files: Files larger than 4GB
• Unicode Filenames: Full Unicode support
• Packet Writing: Incremental disc writing
• Cross-Platform: Supported on multiple operating systems

Performance and Optimization

Creation Optimization

• Buffer Size: Larger buffers for faster creation
• Compression: Optional compression for certain content
• Verification: Built-in integrity checking
• Parallel Processing: Multi-threaded creation when possible

Access Patterns

• Sequential Access: Optimal for streaming data
• Random Access: Acceptable for smaller files
• Caching: Operating system disc cache benefits
• Network Mounting: NFS/SMB mounting for network access

ISO files remain a crucial format for software distribution, system backup, and optical media emulation, providing a standardized way to preserve and distribute disc-based content across different platforms and applications.