"Highly Compressed" ISOs are rarely simple zip files. They are usually "repacks" created by warez groups using specific techniques:
The "Highly Compressed" Yakuza 2 ISO serves as a historical artifact of the internet era. It represents a compromise between accessibility (file size) and artistic integrity (video quality). While modern internet speeds have made 4 GB downloads trivial—rendering the need for compressed ISOs obsolete—the technical ingenuity required to shrink a massive open-world game without breaking it remains an impressive feat of software manipulation.
The most famous versions of the compressed Yakuza 2 ISO were those that managed to fit the game onto a CD-ROM (under 700MB) or onto smaller USB drives for the PS2 Homebrew community (Open PS2 Loader).
Tools like 7-Zip or WinRAR remove "dummy" or "padding" data—empty space used by the original disc to fill capacity—without affecting actual gameplay. How to Extract and Play