Highly compressed PS2 ISOs (often labeled "UPD" for updated or high-compression packs) are designed to minimize storage space, making it easier to download and store large libraries on mobile devices or smaller hard drives
chdman createcd -i game.iso -o game.chd -c lzma -hs 4096 i ps2 highly compressed games iso upd
The current "gold standard". It compresses games significantly while keeping them in a single, playable file. GZIP (.gz): Often used for PCSX2. You can compress an ISO to Highly compressed PS2 ISOs (often labeled "UPD" for