It uses block-based Deflate compression across the entire image.

If you have uncompressed .iso files, you can compress them yourself using , a command-line tool.

Bottom line: "Highly compressed" in this context is a for malware, low quality, or both. Stick to CHD format from trusted tools, not shady download sites.

Double-click the file named CUE or ISO to CHD.bat .

Security and safety

Standard PS2 ISO files contain a massive amount of "dummy data"—empty sectors used by original game developers to optimize disc-reading speeds on physical PS2 hardware. When emulating on modern solid-state mobile storage, this dummy data serves no purpose. Benefits of Compression:

The standard, uncompressed disc image. It offers perfect compatibility but maximum file size.

Occasionally causes micro-stutters on weaker mobile processors because block-by-block decompression requires slightly more CPU power than CHD. 3. PZZ / ISO.GZ Gzip compression creates a .gz file wrapper around the ISO.

: Place the .chd file in your AetherSX2 game folder and rescan. A Note on "Super Compressed" 50MB Files

Don't download pre-compressed files from sketchy sites; it's safer and more reliable to compress your own ISOs using or chdman . Download chdman : This is part of the MAME tools suite. Run the Command : Use createcd to turn your ISO into a CHD.

Fully supported by AetherSX2, but requires a fast storage controller (UFS 2.1 or higher) to avoid loading screen delays. Average Compression Ratios for Top PS2 Titles

Originally created for PSP emulation, it is also supported by AetherSX2. Storage savings: Similar compression ratios to CHD.