While searching for compressed ROMs online, you will likely encounter websites or YouTube videos claiming to offer major Wii games compressed down to 10 MB or 50 MB inside .rar or .7z archives.
: NKit is another lossless format designed for archiving and converting to and from other formats like ISO and GCZ. It is highly specialized for GameCube and Wii disc images and is recognized for its excellent compression ratios and ability to be reverted to a 1:1 original copy. Users have reported reducing a collection of 200 Wii games from 1 TB to just 450 GB using NKit.
When a standard Wii disc is ripped to a computer, it creates a 4.37 GB ISO file. This happens because the console reads data from standard single-layer DVD media.
The Ultimate Guide to Highly Compressed Wii ROMs: Save Space Without Losing the Fun
This is the modern standard created by the developers of the Dolphin Emulator
It strips out all dummy data and padding completely.