: Many PS2 discs contain "dummy" or "padding" data (often just zeros) to fill the disc and keep data at the outer edges for faster physical reading. Highly compressed versions "scrub" this data, which can reduce a several-gigabyte ISO to its actual data size. Ripkits & FMV Downsampling
To understand how a game like God of War (which is roughly 8GB) can be shrunk down, you must understand the difference between a "Full ISO" and a "Highly Compressed" file. highly compressed ps2 games under 200mb upd