Not trying to be rude but the sizes I mentioned are what they took in my hard drive, I didn't say anything about the SD card, I bought a 32GB SD card and I have about 3GB worth of Wiiware and emulators and homebrew stuff on it, my whole GC collection while compressed with GCUtility and compressed as .rar combined together are around 22GB yet when I converted them to the DML format they took exactly 32GB on my hard drive making me only able to copy 75% of my GC games on the 32GB SD while getting yet another 8GB SD only for those few games left, I'm not complaining or anything but I'm only reporting my problem, maybe I'm doing something wrong, idk, but I always choose "compress" when converting the games with DiscEX except for Virtua Striker 2002 since I noticed the game only works when not compressed, I will report that I ripped my own disks and didn't download them off the internet!
Oh, I get it. Yeah, I guess it's not the best use of the term "compress".
All it DiscEX actually does is similar to what GCUtility does. It strips off the padding at the beginning of the disk that the manufacturer added to move the files out to the edge of the disk where it's faster to read. It then ends up smaller and, therefore "compressed".
It doesn't really compress it in terms of the RAR or ZIP compression. I never thought about it but I guess for some reason the resulting image file might be harder for that kind of compression program to really shrink down any further.
I think an actual compressed disk image would be going from ISO format to CISO format. (like what uLoader uses.) I think that's the same as changing from GCM files to GCZ in terms of the Dolphin emulator for PC but, unfortunately, DML doesn't support that. My guess is that it would slow down reading times, too, which is a trade-off many are not willing to make.