The original Xbox 360 used a standard dual-layer DVD. Game devs often filled these discs with dummy data (padding) to ensure faster load times by placing critical data on the faster outer rings of the disc. Compression tools strip this padding, resulting in file sizes that are often 50-70% smaller than the original ISO.
If you are looking to manage your own game backups to save space, here are the legitimate technical methods used by the community. xbox 360 games iso highly compressed
A standard Xbox 360 dual-layer DVD holds roughly 7.9GB of data. While file compression (like .zip, .rar, or .7z) can reduce file size, the data on game discs (textures, audio, video) is often already compressed. The original Xbox 360 used a standard dual-layer DVD