Most "highly compressed" files you download are simply archives. While the download is small, you still need the original amount of space on your hard drive once you extract the ISO. PCSX2 cannot run a .rar or .7z file directly. 2. Compatibility with CSO and CHD Formats
Popular compressed games are re-uploaded constantly. If a single bit of data in a .7z file is corrupted, the extraction fails. Always check if the archive has a recovery record. pcsx2 games highly compressed work