: The ISOs are usually distributed in LZMA2 compression formats (like .7z), which can shrink a 4GB game into a very small download, though the file must be extracted back to its full size (or a slightly reduced CSO/CHD size) to play. Popular Games Often Found Highly Compressed God of War I & II

: Supported by PCSX2; it builds an index on the first load so there is no speed penalty during gameplay. How to Use Highly Compressed ISOs PS2 Android emulator Play! Setup Guide

Search for CHD format . It is lossless (no quality loss) and offers better compression than CSO without reducing video or audio quality. Highly compressed ISO files are usually CSO or custom 7z archives containing stripped data.