Compression Guide

🗜️ Compression Guide

OpenROM can compress and extract ZIP and 7Z archives — useful for archiving ROM collections or sharing files.

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Compression Levels

Level	Speed	Size	Best for
Fast	⚡⚡⚡	Bigger	Quick archiving
Normal	⚡⚡	Balanced	Daily use
Ultra	⚡	Smallest	Long-term archiving

Default is Normal.

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Smart Skip

OpenROM automatically skips files that are already compressed:

CHD, CSO, ZSO, RVZ, ECM, 7Z, ZIP → skipped automatically
ISO, BIN, GDI, IMG → compressed

This prevents double-compression which wastes space and time.

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How to Compress (GUI)

1. Go to the Compress tab
2. Drop your ROM file or folder
3. Pick ZIP or 7Z
4. Pick compression level
5. Click Compress

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How to Compress (CLI)

# Single file to 7Z
openrom-core --compress "game.iso" --format 7z --level ultra
 
# Single file to ZIP
openrom-core --compress "game.iso" --format zip --level normal
 
# Entire folder
openrom-core --compress-folder /roms/ --format 7z --level ultra
 
# Delete source after successful compression
openrom-core --compress "game.iso" --format 7z --delete-source

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How to Extract (CLI)

# Extract ZIP or 7Z (auto-detected)
openrom-core --extract "game.zip"
 
# Extract to specific folder
openrom-core --extract "game.7z" --output /roms/extracted/

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ZIP vs 7Z — Which to Use?

	ZIP	7Z
Compatibility	Universal	Most tools support it
Compression	Good	Better (~30% smaller)
Speed	Faster	Slower at Ultra
Best for	Sharing	Archiving

Recommendation: Use 7Z for archiving, ZIP for sharing.

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Important Note About Disc Images

For disc images (PS1, PS2, GameCube etc.), CHD is almost always better than ZIP/7Z:

• CHD is purpose-built for disc images
• CHD is directly mountable by emulators — no extraction needed
• CHD is typically smaller than ZIP/7Z on disc image content Use ZIP/7Z for cartridge ROMs (SNES, GBA, NDS) or when you need to share files with people who don't have OpenROM.

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→ Conversion Matrix → Format Guide