Disc I/O

Disc image loading and format support for GameCube and Wii games

Dolphin supports multiple disc image formats for GameCube and Wii games with varying compression and features.

Supported Formats

Location: Source/Core/DiscIO/

ISO

Uncompressed 1:1 disc image

Size: 1.4 GB (GC) / 4.7 GB (Wii single-layer)

RVZ

Modern compressed format (recommended)

Size: 200 MB - 1 GB (Zstandard compression)

GCZ

Legacy GameCube compression

Size: 300 MB - 800 MB (Deflate)

WIA

Compressed Wii format

Size: 400 MB - 1.5 GB (LZMA/Bzip2)

WBFS

Wii Backup File System

Size: Variable (scrubbed)

CISO

Compact ISO

Size: Similar to GCZ

Format Comparison

Format	Compression	Speed	Size	Recommend
RVZ	Zstandard	Fast	Best	✅ Yes
ISO	None	Fastest	Largest	For backups
WIA	LZMA/Bzip2	Slow	Good	Legacy
GCZ	Deflate	Medium	OK	Legacy GC
WBFS	Scrubbing	Fast	Good	Limited
CISO	Deflate	Medium	OK	Limited

Recommended: Use RVZ format for best compression and speed balance.

RVZ Format

Dolphin’s modern compression format:

Features

• Zstandard compression (very fast, excellent ratio)
• Block-based (supports partial reads)
• Wii partition decryption
• Hash removal (smaller size)
• Scrubbing support

Compression Levels

# dolphin-tool convert
dolphin-tool convert -i game.iso -o game.rvz \
  -f rvz \
  -c zstd \
  -l 5     # Compression level 1-22

Level	Speed	Ratio	Recommended
1-3	Very fast	OK	Quick conversion
5	Fast	Good	Default
9-13	Medium	Better	Archive
18-22	Slow	Best	Long-term storage

Block Size

# Larger blocks = better compression, slower seeks
dolphin-tool convert -i game.iso -o game.rvz \
  -f rvz -c zstd -l 5 \
  -b 131072  # 128 KB (recommended)

Recommended: 128 KB (131072 bytes)

Disc Volume

Location: DiscIO/Volume.cpp

Common interface for all formats:

// Open any supported format
std::unique_ptr<Volume> CreateVolume(const std::string& path);

// Read sectors
bool Read(u64 offset, u64 size, u8* buffer);

// Get disc info
Platform GetVolumeType();      // GameCube or Wii
Country GetCountry();           # Region
std::string GetGameID();        # 6-char game ID

GameCube Disc Structure

GameCube Disc (1.4 GB)
├── 0x0000: Boot info (game ID, version, etc.)
├── 0x0420: Disc Header Info 2
├── 0x2440: Apploader (game-specific loader)
├── Variable: FST (File System Table)
├── Variable: DOL (main executable)
└── Variable: Game files

Reading Game Files

Location: DiscIO/Filesystem.cpp

Extract files from disc:

// Get filesystem
std::unique_ptr<FileSystem> fs = CreateFileSystem(volume);

// List files
std::vector<std::string> files = fs->GetFileList();

// Extract file  
bool ExportFile(const std::string& path, const std::string& export_path);

Wii Disc Structure

Wii discs use partitions:

Wii Disc (4.7 GB single-layer, 8.5 GB dual-layer)
├── 0x0000: Disc Header
├── 0x40000: Region settings
├── 0x50000: Partition table
├── Partition 0: Update partition (system update)
├── Partition 1: Game partition (main content)
│   ├── Partition header (ticket, TMD, certs)
│   ├── Encrypted content
│   │   ├── 0x0000: Partition info
│   │   ├── 0x0420: Boot info
│   │   ├── Variable: Apploader
│   │   ├── Variable: FST
│   │   ├── Variable: DOL
│   │   └── Variable: Game files
│   └── H3 hash table
└── Partition N: Optional channel/DLC partitions

Partition Encryption

Wii partitions are AES-encrypted:

Location: DiscIO/VolumeWii.cpp

// Decrypt partition data
DecryptPartition(partition_key, encrypted_data, decrypted_data);

• Each 0x8000-byte block is encrypted separately
• 0x400-byte hashes at start of each block (removed in RVZ)
• Title key from ticket + Common key

Scrubbing

Remove unused data:

dolphin-tool convert -i game.iso -o game.rvz \
  -f rvz -s  # --scrub flag

Scrubbing removes:

• Unused partition space
• Garbage data
• Debug information

Reduces size by 10-30%.

WIA Format

Specification: See WIA/RVZ Format Spec

Legacy Wii compression:

Compression Methods

• None: Uncompressed (testing)
• Purge: Remove unused data only
• Bzip2: Good compression, slow
• LZMA: Best compression, very slow
• LZMA2: Improved LZMA

Chunk Size

Data divided into chunks (default 2 MB):

dolphin-tool convert -i game.iso -o game.wia \
  -f wia -c lzma -l 5 -b 2097152  # 2 MB chunks

GCZ Format

Legacy GameCube compression:

Structure

• Deflate compression per block
• Block size: typically 16 KB
• Header with block offsets

GCZ is outdated. Use RVZ for new conversions.

WBFS Format

Wii Backup File System:

Features

• Automatic scrubbing
• Multiple games per volume
• Direct Wii console compatibility (with homebrew)

Limitations

• No compression (but scrubbed)
• No dual-layer support
• Less efficient than RVZ

Disc Conversion

Use dolphin-tool convert for format conversion:

ISO to RVZ (Recommended)

dolphin-tool convert \
  -i game.iso \
  -o game.rvz \
  -f rvz \
  -c zstd \
  -l 5 \
  -b 131072 \
  -s  # Optional scrubbing

Any Format to ISO

# Extract to uncompressed ISO
dolphin-tool convert -i game.rvz -o game.iso -f iso

Batch Conversion

#!/bin/bash
for iso in *.iso; do
  dolphin-tool convert -i "$iso" -o "${iso%.iso}.rvz" \
    -f rvz -c zstd -l 5 -b 131072 -s
done

See DolphinTool Convert for details.

Disc Verification

Verify disc integrity:

# Compute hash
dolphin-tool verify -i game.rvz -a md5

# Full verification report
dolphin-tool verify -i game.wia

See DolphinTool Verify for details.

Performance Considerations

Read Speed

Format affects loading speed:

• ISO: Fastest (no decompression)
• RVZ (Zstandard): Very fast (hardware decompression)
• GCZ/CISO: Medium (Deflate overhead)
• WIA (LZMA): Slow (CPU-intensive decompression)

Recommendation: RVZ for best balance.

Disc Cache

Dolphin caches decompressed blocks:

[Core]
DiskCache = True     # Cache disc reads (recommended)
DiskCacheSize = 32   # MB of cache

Reduces stuttering with compressed formats.

Storage

Typical sizes:

Game	ISO	RVZ (Zstd-5)	Savings
Super Mario Galaxy	4.7 GB	850 MB	82%
Mario Kart Wii	4.7 GB	720 MB	85%
Luigi’s Mansion	1.4 GB	380 MB	73%

See Also

• DolphinTool Convert
• DolphinTool Verify
• WIA/RVZ Format Specification