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

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Supported Formats

Location: Source/Core/DiscIO/

ISO

Uncompressed 1:1 disc imageSize: 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 compressionSize: 300 MB - 800 MB (Deflate)

WIA

Compressed Wii formatSize: 400 MB - 1.5 GB (LZMA/Bzip2)

WBFS

Wii Backup File SystemSize: Variable (scrubbed)

CISO

Compact ISOSize: Similar to GCZ

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Format Comparison

FormatCompressionSpeedSizeRecommend
RVZZstandardFastBest✅ Yes
ISONoneFastestLargestFor backups
WIALZMA/Bzip2SlowGoodLegacy
GCZDeflateMediumOKLegacy GC
WBFSScrubbingFastGoodLimited
CISODeflateMediumOKLimited
Recommended: Use RVZ format for best compression and speed balance.

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RVZ Format

Dolphin’s modern compression format:

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Features

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

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Compression Levels

# dolphin-tool convert
dolphin-tool convert -i game.iso -o game.rvz \
  -f rvz \
  -c zstd \
  -l 5     # Compression level 1-22
LevelSpeedRatioRecommended
1-3Very fastOKQuick conversion
5FastGoodDefault
9-13MediumBetterArchive
18-22SlowBestLong-term storage

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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)

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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

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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

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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);

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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

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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

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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%.

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WIA Format

Specification: See WIA/RVZ Format Spec Legacy Wii compression:

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Compression Methods

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

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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

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GCZ Format

Legacy GameCube compression:

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Structure

  • Deflate compression per block
  • Block size: typically 16 KB
  • Header with block offsets
GCZ is outdated. Use RVZ for new conversions.

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WBFS Format

Wii Backup File System:

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Features

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

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Limitations

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

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Disc Conversion

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

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Any Format to ISO

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

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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.

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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.

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Performance Considerations

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.
Dolphin caches decompressed blocks:
[Core]
DiskCache = True     # Cache disc reads (recommended)
DiskCacheSize = 32   # MB of cache
Reduces stuttering with compressed formats.
Typical sizes:
GameISORVZ (Zstd-5)Savings
Super Mario Galaxy4.7 GB850 MB82%
Mario Kart Wii4.7 GB720 MB85%
Luigi’s Mansion1.4 GB380 MB73%

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See Also