Open your terminal/command prompt.
Let's say you download God_of_War_2.7z and it is 800 MB. When extracted, it will become God_of_War_2.iso at 4.5 GB.
It compresses files significantly and is fully readable by modern emulators. You do not need to extract it to play. Cons: Older emulators do not support it. 3. The CSO Format (.cso)
Highly compressed PS2 ISO ROMs solve this problem. By using advanced compression algorithms, you can shrink game files by up to 40% to 80% without losing any in-game content, textures, or audio.